As the title suggests, I do not understand decibels. Two questions please.

1. Why is it measured as a negative, then "o", then as a positive?

2. Why does my CD's sound good at -25 db and my DVD's in THX 5.1 need -12 to sound good?

Any insight is appreciated.

Well, for DVDs and such there is a reference which if you calibrate to to align with zero, you are then -x db from reference, or at reference or x dbs above reference.

Unless you've calibrated reference level to be zero in your system, it doesn't really matter. And it doesn't matter for music CDs etc.

As for why DVDs tend to be quieter, they often have much larger dynamic range than a lot of music CDs, so the normal sounds (like dialogue) are softer, so you need to listen at a higher volume setting. Then when things get loud, they get REALLY loud. CDs are usually a lot more compressed and tend to be much louder all the time, so you often listen at a much lower volume setting to get the same kind of "regular" spl as you would get for most of the length of a movie for instance. You'll find this may not always be the case, a lot of classical CDs often aren't very compressed and have very large dynamic range so the normal/quiet parts are quite quiet so you may turn them up higher as you might a DVD.

In any case, set the volume dial where things are appropriate for you. And don't listen too loud or you *will* damage your hearing over time.

Here's my take...

1. Because 0 is a reference point - what exactly that reference point is is somewhat controversial. In many setups, the system is (or can be) calibrated so that 0 represents "reference level" playback or 105dB peak levels at the seating position.

So, with the system calibrated in this manner, you can somewhat determine the approximate volume based on the volume position. For example, if 0 of the volume knob equals 105dB and you set the volume to -20dB, you would know that your approximate peak volume is 85dB.

As you observe with respect to question #2, the above statement is not always accurate because there are differences in the output levels of different playback devices. There are also differences in recording levels between various CDs and DVDs. One or the other, or both, of these reasons are why the volume setting is different.

Don't get too hung up on the numbers, merely adjust the volume as necessary.

2. Why does my CD's sound good at -25 db and my DVD's in THX 5.1 need -12 to sound good?
Sorry, but those CD do not sound good at -25 db. In fact they don't sound good at any db. This is a major problem with today's recorded music. They are very very very very very very very compressed. Hence the average sound level is just about equal to the maxium sound level and that's why you are listening at -25 db. It sounds loud most of the time. For some reason, movies are not messed up like this and so to get the average sound level to where you are comforable, you need to crank up the volume. Then the dynamics will sound correct and actually be louder.

Ed

Sorry, but those CD do not sound good at -25 db. In fact they don't sound good at any db.
Ed

You are right, it does not sound good. I just can't go any louder without it sounding worse.

Thank you for all your help.

The dB expresses a ratio of two values.
0 dB (in audio) means no gain, no attenuation...unity.

0 dB (in audio) means no gain, no attenuation...unity.

I know where you are coming from, but do you think that's an accurate statement in the example of a receiver?

it should be

I was thinking since the amps are built into the receiver that 0dB of the volume control doesn't really seem to represent unity gain throughput.

I assume the amps have a fixed gain, and audio level is controlled by the "attenuator".
0dB on the "knob" should mean no gain, or attenuation through the preamp.
Otherwise, what's the point of using that scale?

I assume the amps have a fixed gain, and audio level is controlled by the "attenuator".
0dB on the "knob" should mean no gain, or attenuation through the preamp.
Otherwise, what's the point of using that scale?

Yeah, I agree on the preamp part, however it's the amp part why I questioned the unity gain statement - because, overall, a receiver is far from unity gain when the volume is set at 0dB.

I think that is the OP's question. What is the point of the scale?

It's merely a reference that is only slightly more useful if it's calbrated to match up with some known value. Even calibrated to a known value, it's not absolute because of variances in source levels.

, a receiver is far from unity gain when the volume is set at 0dB

Why?

That just makes the scale meaningless.

Why?

That just makes the scale meaningless.

Because...

To me, unity gain means the level out is the same as the level in.

If one puts 1 volt into a receiver input, sets the volume control at 0dB, there is going to be much more than 1 volt at the speaker terminals.

Perhaps we just have a different opinion of what unity gain implies with respect to a receiver as a total package vs. looking at it as individual subassemblies.

To me, unity gain means the level out is the same as the level in.

Yes, for the preamp.



If one puts 1 volt into a receiver input, sets the volume control at 0dB, there is going to be much more than 1 volt at the speaker terminals.

1 Volt out of the preamp, and into the power amp section, with a fixed gain, could result in full power outut of the power amp, if the power amp had a sensitivity of 1V, for example.

You may be surprised how many components are not even close to the reference levels listed on the silkscreened numbering on volume controls.

Regardless of how the decibel is used, remember that it is a unit of power level, in this case, a sound wave or electrical signal in recording..the fundemental unit for the measurement is the "bel" so a decibel is .1 of a bel. The important part to remember is that it is measured on a logrithmic scale ;
If we apply it to sound waves and the threshold of hearing is 0 than 10 db is ten times that power level or 10 times as loud. Scary when you think of a increase of that magnitude....I wouldn't want to be listening to anything at a 105 db level when hearing damage can occur at 90 db (sustained over time); and once damage occurs, it's gone for good. Not a bad idea to stick a sound pressure meter in your kids ear buds and educate them as to the possible danger of listening to I Pods all day.

Regardless of how the decibel is used, remember that it is a unit of power level,

No. dB is not a unit, it is a ratio, and can be used to describe relationships between many different things of various units.

No. dB is not a unit, it is a ratio, and can be used to describe relationships between many different things of various units.

You may be talking about the conversion function 10 log(base10)times the ratio of P to P sub 0 (where p is given in db) and P sub 0 is your reference power....there is a ratio in the conversion function but a db IS a unit measure in the same vain as a foot and meter are unit measures. If it's not a unit measure than I messed that up for my kids in the 25 years I taught log functions in precalc.
Having something as a ratio does not by the way prevent it from being a unit measure.....like say Ft/lbs, miles per hour, ft per second.....need I say more.

You may be talking about the conversion function 10 log(base10)times the ratio of P to P sub 0 (where p is given in db) and P sub 0 is your reference power....there is a ratio in the conversion function but a db IS a unit measure in the same vain as a foot/meter are unit measures. If it's not a unit measure than I messed that up for my kids in the 25 years I taught log functions in precalc.
Having something as a ratio does not by the way prevent it from being a unit measure.....like say Ft/lbs, miles per hour, ft per second.....need I say more.

Well, I hate to say it, but you are incorrect about that. dB is not at all like miles, or miles per hour, etc. It is dimensionless.

I was too quick before, it's not accurate to say that dB is not a "unit" but it is dimensionless, which is usually what "units" refer to, as in a unit of measurement which is a unit with a dimension, such as miles. dB has no such dimensions, and can be used to describe the relationships between all kinds of different things, from sound pressure, to sound intensity, to sound power, to voltage, to light intensity, etc etc etc.

It is not at all comparable to things like feet and meters, which have dimensions.

dB by itself is a ratio. When we add a reference like dBa, dBm or dB SPL then it has a dimension.

[QUOTE=ChrisWiggles]Well, I hate to say it, but you are incorrect about that. dB is not at all like miles, or miles per hour, etc. It is dimensionless.

Ahhhhhh.....OK, so you're
the young man in the front row that needs every word defined.
Here goes.....miles per hour is the ratio of miles traveled to distance (one mile); one unit is time and the other is distance.....together they are another unit measure....what does dimension have to do with it if your refereing to length, width and depth.....there are other unit measures like say....Watts which is Volts times Amperes., they are all unit measures.
So some unit measures have "dimension" if you mean measurable in length, some do not, like volts.....you need a volt meter to measure that.....so I guess it's non dimensional
? I prefer not to even bring in the term dimension.....it limits the discussion....by your restrictions. So db measures sound level as a unit measure, miles measure distance as a unit measure, watts measure electricity as a unit measure etc. and some unit measures are ratios; and some are not..........

Do you know you're PO ing my wife who has to help me get the spelling correct enough for the spell check to work !!!!!!

dB by itself is a ratio. When we add a reference like dBa, dBm or dB SPL then it has a dimension.
Enlighten me; the ratio of what to what. Remember you must name two "different" items that can be written as a fraction to equal one db. measure. .....Identify what each letter stands for, d is deci and b is bel, a decibel is .1 of a bel which is a unit measure.......now say what a, m, spl, stand for .....

Please.....someone with an engineering degree, jump in here and help me......

So db measures sound pressure as a unit measure

No, it most certainly does not.

If you are interested in sound pressure, the units are N/m^2
If you are interested in sound intensity, the units are W/m^2
If you are interested in sound power, the units are W
You could also be interested in things like volts, or various other units.

Note that none of the above units are "dB."

dB can be used to describe all of the above. dB does NOT equal some units of "sound pressure level." dB can just as easily be used to describe voltage gain or things like that, which have nothing to do with SPL. As such, it should be clear that dB has no dimensions, and is not at ALL comparable to something like miles per hour, or seconds, or kilograms.

When you say "miles per hour" you are using the units: miles/hour. You could also describe miles/hour using a decibel scale if you wished. You could describe the number of words in this post with decibles, or the mass of something using decibels, or whatever quantities you wanted.

edit: The closest comparison that I can draw which people are commonly familiar with is percent. Percent has no dimensions, it is just a number that relates two things. dB is similar in this way, and can be used to relate any of various kinds of quantities whenever it is more convenient to express things in this manner.

H.....MMMMMM....you mean because I use a meter for length..., I can't use another unit of measure for length....I guess you flat refuse to read my ENTIRE definition of db...now I'm holding in my hand, a device called a sound level meter....and gee, the unit measure is in db.....funny, Id better trade it in....strictly speaking, the pressure from the sound waves is converted to a db reading for sound level which is directly directly related to sound pressure.

Remember a db is a unit of POWER, usually of a sound wave or electrical signal....when I get into a disscussion with one person and use a db as a unit of of power measuring sound, you can jump in and say it's something else when used as a unit of power for an electrical signal....you guys are picking and choosing your narrow points of view and just throughing darts and hope something sticks....nad remember....your whole premise is based on a db is not a unit measure......

By the way....the bel in decibel is named after Alexander Grahm Bell.......I think he had electricity and sound level in mind and not words in this paragraph......ya think....

http://en.wikipedia.org/wiki/Decibel

I'm by no means an expert in this, but the point you are missing in the example of the sound meter is that dB(SPL) is different than dB.

"I'm by no means an expert in this, but the point you are missing in the example of the sound meter is that dB(SPL) is different than dB"

I agree, and the original question was......what's a decibel....what ever sufix you add, I'm going to guess, is an application of the db.....but it's still a unit measure...read the above edit....Alexander Graham Bell; the bel in decibel.

Some dB reference levels:
dBk - 1 kilowatt
dBm - 1 milliwatt, 600 ohms
dBv - 1 volt
dBw - 1 watt

Or in other things:

80 horsepower/ 50 horsepower is 2dB

In a water line:

80 psi / 63 psi is 2dB

horsepower is the same equation as watts
psi is the same equation as volts

H.....MMMMMM....you mean because I use a meter for length..., I can't use another unit of measure for length....I guess you flat refuse to read my ENTIRE definition of db...now I'm holding in my hand, a device called a sound level meter....and gee, the unit measure is in db.....funny, Id better trade it in....strictly speaking, the pressure from the sound waves is converted to a db reading for sound level which is directly directly related to sound pressure.

The meter you are holding is measuring sound pressure level. The units for sound pressure level are pressure, or force per unit area. This is usually described using newtons per unit area(or pascals). Because the audible range is so ridiculously huge, it is not at all intuitive to directly quantify SPL using these units, as such it is usually expressed as a RATIO between the measured sound pressure level and an assumed reference, which is the audible threshold or 2x10^-5 N/m^2.

Remember a db is a unit of POWER, usually of a sound wave or electrical signal....when I get into a disscussion with one person and use a db as a unit of of power measuring sound, you can jump in and say it's something else when used as a unit of power for an electrical signal....you guys are picking and choosing your narrow points of view and just throughing darts and hope something sticks....nad remember....your whole premise is based on a db is not a unit measure......

You are mistaken. dB is not a unit of power at all. In fact, your post illustrates this quite well. You just finished described measuring Sound Pressure Level using a meter which reads in dB. Sound Pressure Level is not a measure of power. Sound Power is measured in Watts, Sound Pressure is measured in N/m^2. These are two very different things. Yet dB can be used to quantify both of them. This disproves your claim that dB is a specific unit of measurement that quantifies a specific thing, since clearly it can be used to express both power, and sound pressure level. In addition, it can be used to describe any other numerical relationship.

The reason is because dB is merely a ratio used to describe a relationship between two numerical values. Those values could be describing anything, including things like power and sound pressure level. Other things dB commonly describe are things like volts, sound intensity level,

I'm not picking and choosing, or making things up. It may seem academic to pay attention to these differences which may for most people seem immaterial, but if you're going to assert things as being factually so, you should know what you're talking about. It doesn't bother me that people don't worry themselves with technical accuracy or what may seem like minutiae, but if you are going to make statements about these particulars you should strive to try to make those statements factually correct.

You are mistaken in your understanding of decibels, and I hope you come to understand that decibels merely express a ratio between two values. This relationship has no units, and decibels can be used to describe values of various kinds.

The premise is that dB is not a unit of measurement, because it is not. It is merely a ratio. That most people don't correctly understand this does not mean it isn't so.

Enlighten me.....I'm still waiting for the ratio of two quantities that a db is suppose to equal......I keep hearing ratio, ratio, ratio, and no one will tell the two quantities this ratio is that equals the unit measure of a db.......that you say is not a unit measure after you indicated maybe it was after you said it wasn't......A ratio is like miles per hour where per is exactly the same as a fraction bar...as in mile/hour....so what is the db the ratio of ?

"I'm by no means an expert in this, but the point you are missing in the example of the sound meter is that dB(SPL) is different than dB"

I agree, and the original question was......what's a decibel....what ever sufix you add, I'm going to guess, is an application of the db.....but it's still a unit measure...read the above edit....Alexander Graham Bell; the bel in decibel.

The Bel is simply:

log (value1)/(value2)

The deciBel is 1/10 of that or:

10 log (value1)/(value2)

In neither case are do units remain, because whatever the units are for value 1 and value 2, they cancel.

It's the same thing with percent, which is another unitless way to quantify a relationship between values. Precents can be used with numerical values of any units, and a number in percent does not have dimensions, it is merely a relationship.

Enlighten me.....I'm still waiting for the ratio of two quantities that a db is suppose to equal......

What do you mean? dB does not equal anything, that is the point. dB is just a WAY of expressing a relationship between two numbers.

In the same vein: could you tell me what percent equals? What are the units of percent? What can I measure with percent? When I say that I have 50%, what does that mean? What do I have 50% of?

They are very very very very very very very compressed.

I think you forgot a "very" in there somewhere :-) The sad thing is that the main two reasons this is true is FM radio and crap stereo systems (such as cars, exercise mp3 players, etc).


mconno: dB is used to relate measurements in a vast range of applications. For example, for line-level voltage signals, you usually use dBV (or dBu). For sound loudness, you typically use dB(SPL) (which is relative to the assumed 0 dB audibility threshold).

Or, to put it another way: when you go to a tape recorder and calibrate the VU meters, they will be calibrated in dB -- relative to the assumed saturation point of the tape. Clearly, this voltage is not related to sound pressure in air. When you measure antenna sensitivity, you measure in dB relative to a reference antenna. Clearly, this is not related to sound pressure in air (or saturation of tape, for that matter). When you measure sound pressure level (as in a concert venue), you measure in dB relative to the audibility threshold. When you mix music on a mixer, the faders are labeled in dB relative to unity gain (where unity gain is defined as a certain voltage into a certain impedance output). Typically, your Mic input will give you 40 dB gain (because microphones are very weak signal sources); your fader will give you between minus infinity (quite) and plus 12 (loud). Your busses and main outs will then give you the same amount of gain, so that the maximum voltage gain you can get is about 76 dB (voltage).

I believe that a human can sing at 80 dB SPL (say, an opera singer). This would mean that, played at reference level all the way through for all the different systems, from SPL at the microphone, to voltage in the mixer board, to saturation of the tape, to gain in the pre-amp, to gain in the power amp, to sensitivity in the speakers, to mode gain in your listening room, that human would be played back at 80 dB SPL. Because the manufacturer of the receiver cannot know what calibrations were made in recording, mixing, mastering, transmission or decoding, they cannot calibrate the volume knob to in-air SPL. Instead, they calibrate the knob to "peak performance" of the power amp -- when your receiver says 0 dB, it allegedly is working as efficiently as it can to play undistorted music into the air, whatever loudness that actually happens to be.

Sorry my man...you can't get out of it that easy....all your doing is restating my function I gave way back when, how you evaluate power.....10log(base10)times(p/PsubO) is not a ratio, it's a function for evaluating a power in db which is a unit of power level for measuring sound level or electrical signal....I'm still waiting for a real live ratio.....just a simple ratio and 10 times the common log of a ratio is not a ratio. So I must conclude that db are logarithmic functions that increase exponential, if they were a ratio, they would increase linearly......

This discussion is now ended....I'll be back for advise on speakers...just don't mention db.

Sorry my man...you can't get out of it that easy....all your doing is restating my function I gave way back when, how you evaluate power.....10log(base10)times(p/PsubO) is not a ratio, it's a function for evaluating a power in db which is a unit of power level for measuring sound level or electrical signal....I'm still waiting for a real live ratio.....just a simple ratio and 10 times the common log of a ratio is not a ratio. So I must conclude that db are logarithmic functions that increase exponential, if they were a ratio, they would increase linearly......

This discussion is now ended....I'll be back for advise on speakers...just don't mention db.

Man I'm glad you aren't a student of mine.

You've had numerous people try to explain this to you, but instead you just avoid the issue, and then try to end the discussion. Do you even care if you are correct or not? I would hope you would be interested in knowing what the truth was, because you are asserting things contrary to any textbook I've seen. I have two acoustical texts in front of me right now that explain this quite clearly. Even wikipedia gets it correct.

10log(base10)times(p/PsubO) is not a ratio,

"p/Psubo" IS a ratio...you wrote it yourself.

Your "type" is always entertaining ;)

Man I'm glad you aren't a student of mine.

You've had numerous people try to explain this to you, but instead you just avoid the issue, and then try to end the discussion. Do you even care if you are correct or not? I would hope you would be interested in knowing what the truth was, because you are asserting things contrary to any textbook I've seen. I have two acoustical texts in front of me right now that explain this quite clearly. Even wikipedia gets it correct.

Now you guys are misquoting me and adding your own words to make youselves look good; pitiful.......The problem is, you have two "acoustic texts" in front of you.....if they have a glossary....look up decibel, get a "real science book", look it up, get a dictionary.....look it up, have your tried that ?....get a math book that discribes log function, which are the inverse of exponential.....The original point was....an increase of 10 db is ancrease in sound level or electric signal by a factor of ten.....you guys don't know basic math concepts.....you can even say that a db is a uniy measure....and you use "dimension" like some esoteric hogwash. You guys can't even agree on your own definitions....... You don't get it and all you want to do is say...."your wrong".......someone out there has to be wrong cause you're not agreeing wth eachother......And these texts you have say a db is NOT a unit measure....Do you know what another extonential function might look like...say the Richter Scale from (1 to 10) used to express the magnitude of energy of an earth quake....where an increse of just one unit represents a many fold increase in energy (60 times) I believe...that's a unit measure as well. By the way, scale using units to measue quantities is a unit measure. For .....sake just "Google decibel" and read several publications.
The whole point is.....
That care should the taken when working with exponential functions..as small increases on the measurement scale (db or Richer) kead to many times that in increase inlevel or power...distortion can occur rapidly (ex. db used with electric signals in recording levels0 and hearing damage can occur easily if not mindful or increase in sound level......That was the entire premise.....you guys are in your glory telling people they ar wrong on this post and spouting theories you don't have a clue...get out of you "aidio text" and get a science text......you may actually find they agree. I asked for someone with an engineering degree....no rsponse...that tells all. How about any science or math majors out there....with a college degree.

So crawl back into your audio caves and pretend the rest of the word doesn't exist like real math...heck, you've been so unconvincing, I may just start listenning to Bose Speakers..if you're aginst them they MUST be good.

You're angry because you were shown how wrong you are by multiple posters.
Grow a ball or two, and accept that you don't understand what a decibel is, and you may learn something here.

" The decibel (dB) is used to measure sound level, but it is also widely used in electronics, signals and communication. The dB is a Logarithmic unit used to describe a RATIO. The ratio may be power, sound pressure, voltage or intensity or several other things. Later on we relate dB to the phon and the sone (other units related to loudness). But first, to get a taste for logarithmic units, let's look at some numbers. (If you have forgotten, go to What is a logarithm?)"

Is this where you guys get the word ratio from. this is a quote from an audio publication...
Notice the words "is a logarithmic unit"... the word ratio is use a quantitive value that the db unit represents......like any numerical values can be a ratio...example...an incease or 20 db is an increase of 10^2 fold in sound level, or 100 times as great....or 100/1 increase, that's what all these ratios came from.......I believed we have common ground if you can believe one of your own sources...It is a unit measure, it is an exponential function, not a ratio, but it is used to eveluate ratios......the number you get, like all measure ment quantities can be written as ratios......35 miles per hour is 35 miles for one hour. An increase of one on the Richter scale is a increase of madnitude by 60 fold(don't hold me to this value,from memory) or 60 to one increase over the previous measuremnet unit...there's your ratio....60 to 1
So db is used to EVALUATE OR DISCRIBE a ratio.....but IT is not a ratio...So to keep saying a db is a ratio is incorrect....it's used to eveluate values that are expressed as ratios in audio....

By the way Wikipedia has in wrong (not the first time) in the use of the word IS...trust the rest of the journals in audio that use the words evaluate or discribe ratios...and there are plenty...And by the way, I proposed that earlier as possible grounds for disagreement way back when I said P/Psubo the value you are looking for is written as a ratio.....I kept saying that, but I guess there was too much fluff in the way...that a db is 10common log of a ratio.

You're angry because you were shown how wrong you are by multiple posters.
Grow a ball or two, and accept that you don't understand what a decibel is, and you may learn something here.

You silly little twit...you think I'm angry.....pity might be more appropiate...read on; as name calling and vugarity shows you for what you are.....

You silly little twit

read on; as name calling and vugarity shows you for what you are.....

You show your true colours ;)

Despite all the shouting, you haven't actually directly answered mconno's quite simple question: what ratio does a decibel represent?

And the answer is 1dB = 10^0.1, or roughly 1.26.

That's a bit awkward. In practice, the numbers everyone remembers are:

3dB roughly equals a factor of 2
6dB roughly equals a factor of 4
10dB exactly equals a factor of 10
20dB exactly equals a factor of 100
30dB exactly equals a factor of 1000
...and so on.

Unfortunately, decibels are sometimes defined in a slightly different way, depending on whether you're talking about power/intensity or amplitude measurements. For amplitude the scale looks like this:

1dB roughly equals a factor of 1.12
6dB roughly equals a factor of 2
12dB roughly equals a factor of 4
20dB exactly equals a factor of 10
40dB exactly equals a factor of 100
...and so on.

SPL measurements use the former scale.

What is a dB, or 0 dB, or -3dB?
Compared to what?... is that dBm, dBFS, or dBSPL (LeqA), ..ect

SMPTE RP155 (-20dBFS = 0 VU = +4dBu) or 1.23V RMS
EBU R68 (-18dBFS = 0 VU = 0dBu) or .775V RMS

dBV – Decibels relative to 1 Volt RMS.
dBm – Decibels relative to 1 mW (milliwatt).
dBu – Decibels relative to 0.775 Volts RMS.

Until “0” is defined, the relative +/- magnitude is unknown. Here is an analogy,

Question: Is your wife good looking?
Answer: Compared to who?

Yes, but regardless of what you're reference point is, a 1dB increase represents a factor of 1.26. And a 1% increase represents a factor of 1.01. That's part of what he was asking (I think), and he wasn't getting an answer.

Not that it'll help, as everyone seems to be trying to quibble over whatever minor point they can find, due to mconno's attitude problem, and people rising to the bait...

Now you guys are misquoting me and adding your own words to make youselves look good; pitiful.......The problem is, you have two "acoustic texts" in front of you.....if they have a glossary....look up decibel, get a "real science book", look it up, get a dictionary.....look it up, have your tried that ?

Yes I have tried that. I won't type out the whole sections that deal with deciBels, but here are some definitions.

First, from Scienc of Sound 3rd ed.

decibel. A dimensionless unit used to compare the ratio of two quantities (such as sound pressure, power, or intensity), or to express the ratio of one such quantity to an apprpriate reference.

In section 6.1:
"Decibel scales are widely used to compare two quantities. We may express the power gain of an amplifier in decibels, or we may express the relative power of two sound sources. We could even compare our bank balance at the beginning with the balance at the end of the month. ('My bank account decreased 27 decibels last month.') The decibel difference between two power levels, deltaL, is defined in terms of their power ratio W2/W2: deltaL= L2-L1=10 log W2/W1."

In the Appendix we find the following:
'Sound pressure level (Lsubp), sound intensity level(LsubI), and sound power level(LsubW) are all measured in decibels. The formulas are as follows:

LsubP = 20 log p/p0 p0= 2x10^-5 N/m^2

LsubI = 10 log I/I0 I0= 10^-12 W/m^2

LsubW = 10 log W/W0 W0=10^-12 W

Moving to another text: Sensation and Perception: An integrated approach
4th ed, we find:

"Decibels are not absolute, fixed units like inches, grams, or Watts. When we specify a sound in decibels we mean that it is a certain number of times greater or less than some other pressure--the reference pressure, P(r). The decibel scale, using the presumed threshold reference pressure of 0.0002 dynes/cm^2, is conventionally termed sound pressure level (SPL)." (emphasis in text).

Moving to a third text: Master Hanbook of Acoustics 4th ed.

We find a definition in the glossary:
decibel: the human ear responds logarithmically and it is conventient to deal in logarithmic units in audio systems. The bel is the logarithm of the ratio of two powers, and a decibel is 1/10 bel.

We also find a chapter dedicated to sound levels and the decibel:

"A level is a logarithm of a ratio. A level in decibels is ten times the logarithm to the base 10 of the ratio of two power like quantities.

Decibels
A power level of a power W1 can be expressed in terms of a reference power W2 as follows: L1 = log W1/W2 bels. ... Equation 2-2 applies equally to acoustic power, electric power, or any other kind of power.

Two tables follow which list the following which are commonly described using decibels:

Acoustic Power
Acoustic intensity
air particle velocity
pressure
Electric power
current
voltage
distance




....get a math book that discribes log function, which are the inverse of exponential.....The original point was....an increase of 10 db is ancrease in sound level or electric signal by a factor of ten.....you guys don't know basic math concepts.....you can even say that a db is a uniy measure....and you use "dimension" like some esoteric hogwash. You guys can't even agree on your own definitions....... You don't get it and all you want to do is say...."your wrong".......someone out there has to be wrong cause you're not agreeing wth eachother......And these texts you have say a db is NOT a unit measure....

That is correct. I just provided three examples which describe what a decibel is. It is the logarithm of a ratio between two quantities. As such, it is not a fixed unit, i.e. it does not have dimensions.

Do you know what another extonential function might look like...say the Richter Scale from (1 to 10) used to express the magnitude of energy of an earth quake....where an increse of just one unit represents a many fold increase in energy (60 times) I believe...that's a unit measure as well. By the way, scale using units to measue quantities is a unit measure. For .....sake just "Google decibel" and read several publications.

Did you google and read about decibels? Because there are many references available on the internet which also explain this, including:

http://en.wikipedia.org/wiki/Decibel


The whole point is.....
That care should the taken when working with exponential functions..as small increases on the measurement scale (db or Richer) kead to many times that in increase inlevel or power...distortion can occur rapidly (ex. db used with electric signals in recording levels0 and hearing damage can occur easily if not mindful or increase in sound level......That was the entire premise.....you guys are in your glory telling people they ar wrong on this post and spouting theories you don't have a clue...get out of you "aidio text" and get a science text......you may actually find they agree. I asked for someone with an engineering degree....no rsponse...that tells all. How about any science or math majors out there....with a college degree.

I just cited three textbooks which explain what a decibel is. I have studied acoustical science at a university, and while my degree is not in math or physics, that really is irrelevant to the question here. It is not my word against your word, it is the word of the texts that have been cited against your word.

So crawl back into your audio caves and pretend the rest of the word doesn't exist like real math...heck, you've been so unconvincing, I may just start listenning to Bose Speakers..if you're aginst them they MUST be good.

It is real math. It's real science. Perhaps you should study it a little bit before you go on some childish tirade against people who might point out that your thinking on a subject that you are not very familiar with is errant. An honorable thing to do would be to apologize to myself and others at whom you've ranted. If you don't want to believe what is commonly defined as a decibel, then thats your perogative, but I suggest you keep your opinions that the earth is flat to yourself, especially in a domain where there are many people experienced in fields you are unfamiliar with.

Also, you still have not addressed my question above:

In the same vein: could you tell me what percent equals? What are the units of percent? What can I measure with percent? When I say that I have 50%, what does that mean? What do I have 50% of?

There is no disagrement as to the definition of a db. All your definitions refer to it as a "unit" measure which I have always maintained. and many of you have not you .....that it is the log of a ratio...which we agree, and that once evaluated it represents a defined ratio which I have stipulated...is often the case.
You keep saying what a decibel is "used for" I keep agreeing: comparing two quantities and that is a primary use in science....there is agreement....because hearing, as your definition says, is a log function, that's what Bell had in mind.
I'll end, with a shovel may be used to dig a hole......but a shovel is not a hole....the disagreement we have is the same that math majors have with field majors all the time; we use strick definitions....you use applied definitions...your definition works for you, mine is not incorrect as yours is not; because as you want to use my definition in your context it becomes confusing to a field major....if you look at math texts; physical science texts as well as your own, you might not only appeciate the difference but celebrate it. By the way, you didn't appreciate me injecting humor into the discussion, no more than I appreciate some of you injecting vulgarity. I apologize for the both of us.
.Have a nice day !

Despite all the shouting, you haven't actually directly answered mconno's quite simple question: what ratio does a decibel represent?

And the answer is 1dB = 10^0.1, or roughly 1.26.

That's a bit awkward. In practice, the numbers everyone remembers are:

3dB roughly equals a factor of 2
6dB roughly equals a factor of 4
10dB exactly equals a factor of 10
20dB exactly equals a factor of 100
30dB exactly equals a factor of 1000
...and so on.

Unfortunately, decibels are sometimes defined in a slightly different way, depending on whether you're talking about power/intensity or amplitude measurements. For amplitude the scale looks like this:

1dB roughly equals a factor of 1.12
6dB roughly equals a factor of 2
12dB roughly equals a factor of 4
20dB exactly equals a factor of 10
40dB exactly equals a factor of 100
...and so on.

SPL measurements use the former scale.

Thanks....and 40 db=10^(40/10) etc. or db=10^(db/10)
You must have a math background .

A 1dB increase represents a factor of 1.26. And a 1% increase represents a factor of 1.01.KMO well said, your post was succinct, and my post was redundant info, sorry about that.

The term decibel does not in itself indicate power, but rather is a ratio or comparison between two power values. It is often desirable to express power levels in decibels by using a fixed power as a reference.

By remembering just three basic values such as one, three, and 10 dB, the others can easily be obtained without a calculator by addition and subtraction of dB values and multiplication corresponding ratios. i.e.

A 7 dB increase in power (3+3+1) dB is an increase of (2 x 2 x 1.26) = 5 times

A 7 dB decrease in power (-3-3-1) dB is a decrease of (0.5 x 0.5 x 0.8) = 0.2.


FWIW I don't see that you or mconno need lecturing by anyone, especially by the likes of Chris anyway :)

http://en.wikipedia.org/wiki/Decibel

I'm by no means an expert in this, but the point you are missing in the example of the sound meter is that dB(SPL) is different than dB.


The decibel (dB) is an expression of the relationship between a variable quantity and a known reference quantity. There are two different, related, usage dependent, formulas used to calculate decibels and this duality can cause problems for those who do not understand the two different applications and their relation. Since decibels express a relationship between a variable and a known reference, they are useful for a wide variety of measurements in acoustics, physics, electronics and other disciplines


i am assuming that they (in red print) is describing a decibel. and it says clearly "usefu for a wide variety of measurements (WHICH TO ME WOULD BE A UNIT OF MEASUR)


decibel -- Encyclopædia Britannica
decibel (dB), unit for expressing the ratio between two amounts of ... Decibel. one tenth of a bel; unit of measure of loudness of sounds to normal human ears; ...www.britannica.com/eb/article-9029698/decibel


http://www.thereminvox.com/article/view/170/1/37
bel (symbol B) is a unit of measure of ratios; (such as power levels and voltage levels). It is mostly used in telecommunication, electronics, and acoustics. Invented by engineers of the Bell Telephone Laboratory, it was originally called the transmission unit or TU,

... In practice, the numbers everyone remembers are:

3dB roughly equals a factor of 2
6dB roughly equals a factor of 4
10dB exactly equals a factor of 10
20dB exactly equals a factor of 100
30dB exactly equals a factor of 1000
...and so on.

Unfortunately, decibels are sometimes defined in a slightly different way, depending on whether you're talking about power/intensity or amplitude measurements. For amplitude the scale looks like this:

1dB roughly equals a factor of 1.12
6dB roughly equals a factor of 2
12dB roughly equals a factor of 4
20dB exactly equals a factor of 10
40dB exactly equals a factor of 100
...and so on.

SPL measurements use the former scale.

Unfortunately, the acronym SPL by itself is ambiguous. It appears (in the absence of other information) as if SPL could be "sound pressure level" or "sound power level". According to Wikipedia articles linked at bottom of this message, the standard definition of the acronym SPL is "sound pressure level", not "sound power level". SWL is the acronym for "sound power level". Therefore SPL measurements use the second (amplitude) scale given by KMO.

The acronyms are slightly less confusing and easier to remember if we think of them in connection with the names of the physical units, Watts (for power) and Pascal (for air pressure, or pressure in general).

SPL -> Sound Pressure (Pascals) Level
SWL -> Sound Power (Watts) Level
And there is also:
SIL -> Sound Intensity Level
where Intensity = Power per Unit Area (Watts/meter^2)

Why did this multiple notation get started, sometime basing the dB scale on units of power (Watts), sometimes on units of intensity (Watts/meter^2), and sometimes on units of air pressure (Pascals)? Pressure, intensity, and power are all important physical properties of sound waves. Sometimes it is most important to talk about the "pressure deviation from the local ambient pressure", which is the amplitude of the sound wave at a particular location. Sometimes it is most important to talk about the intensity, which is the energy per unit area per unit time carried by the sound wave at a particular location. (Note: the sound intensity at a particular location is proportional to the square of the sound pressure (deviation from ambient pressure) at that location.) And sometimes, it is most important to talk about the power, which is the total energy per unit time radiated from a source of sound, such as a loudspeaker. (Sound power has an integral relation to sound intensity, in other words, the sound power can be obtained by integrating over the sound intensities at different locations on a closed surface that contains the source.)

As an example, we might write, "The discussion about the meaning of deciBels started calmly enough, but soon degenerated into a high SPL shouting match" if we wanted to emphasize that the shouting was causing unusually large (compared to normal volume conversation) fluctuations in the air pressure in the room.

On the other hand, we might write, "The discussion about the meaning of deciBels started calmly enough, but soon degenerated into a high SWL shouting match" if we wanted to emphasize that the shouting was causing an unusually large (compared to normal volume conversation) amount of energy to travel around the room. ;)

http://en.wikipedia.org/wiki/Sound_pressure_level

http://en.wikipedia.org/wiki/Sound_power_level

(edited in response to suggestion to clarify relation between power and intensity)

Why did this "dual" notation get started, sometime basing the dB scale on units of power (Watts) and sometimes on units of air pressure (Pascals)?
SPL is measured from a perspective, for example a mic.

A sound power level (SWL) on the other hand is a measure of the total noise radiated in all directions.

http://www.sizes.com/units/index.htm

here is a list of weights and measures from the website International Committee for Weights and Measures

bel, deci and decibel are all units

bel, deci and decibel are all units

What is "deci" a measure of?

SPL is measured from a perspective, for example a mic.

A sound power level (SWL) on the other hand is a measure of the total noise radiated in all directions.

That's a good point. Actually, still another kind of "sound level" is defined, sound intensity level (SIL), where intensity is power per unit area (watts/meter^2). Both sound intensity level (SIL) and sound pressure level (SPL) are "measured from a perspective". SIL refers to the intensity of the sound at a particular location in the room, SPL refers to the amplitude (pressure deviation) of the sound at a particular location.

I found a link (from Wikipedia) to this nifty calculator:
http://www.sengpielaudio.com/calculator-soundlevel.htm

"Conversion of sound units (levels) •
sound level SPL → sound pressure p and sound intensity I,
sound pressure → sound level,
sound intensity → sound intensity level"

http://www.sizes.com/units/index.htm

here is a list of weights and measures from the website International Committee for Weights and Measures

bel, deci and decibel are all units

You are not correct about your reference. That website is not the International Committe for Weights and measures, this is:

http://www.bipm.fr/en/home/

The SI base units are the following:

m, kg, s, A, K, mol, cd

decibel is not an SI unit of measurement. It is a unit, and it is a very useful one, but it does not have a dimension, i.e. you cannot measure decibels. You can measure things using a unit with dimensions and then EXPRESS that using decibel units.

What is "deci" a measure of?

In SI, the decimal submultiplier prefix meaning 1/10. BTW i dont work for weights and measures, the ruling department on units of measure. i'm just suppling their info for you.

Targus if you are so smart about everything why dont you go and start your own weight and measures company. i'm sure you could get chris w to go with you.

You are not correct about your reference. That website is not the International Committe for Weights and measures, this is:

http://www.bipm.fr/en/home/

The SI base units are the following:

m, kg, s, A, K, mol, cd

decibel is not an SI unit of measurement. It is a unit, and it is a very useful one, but it does not have a dimension, i.e. you cannot measure decibels. You can measure things using a unit with dimensions and then EXPRESS that using decibel units.

in your own quote "It is a Unit". not all units of measure are SI but some outside of SI are APPROVED

"decibel
One-tenth of a bel. Symbol, dB, but see below. (Though the decibel is not an SI unit, the SI convention that a letter representing a person's name in a symbol is capitalized is observed with this unit. The B is for Alexander Graham Bell.) A unit used in electrical engineering and acoustics to express on a logarithmic scale the ratio between two values with the same dimensions"


http://physics.nist.gov/cuu/Units/outside.html
Units outside the SI

Certain units are not part of the International System of Units, that is, they are outside the SI, but are important and widely used. Consistent with the recommendations of the International Committee for Weights and Measures (CIPM, Comité International des Poids et Mesures), the units in this category that are accepted for use with the SI are given in Table 6.

--------------------------------------------------------------------------------
Table 6. Units outside the SI that are accepted for use with the SI
--------------------------------------------------------------------------------

Name Symbol Value in SI units
minute (time) min 1 min = 60 s
hour h 1 h = 60 min = 3600 s
day d 1 d = 24 h = 86 400 s
degree (angle) ° 1° = ( /180) rad
minute (angle) 1 = (1/60)° = (/10 800) rad
second (angle) 1 = (1/60) = (/648 000) rad
liter L 1 L = 1 dm3 = 10-3 m3
metric ton (a) t 1 t = 103 kg
neper Np 1 Np = 1
bel (b) B 1 B = (1/2) ln 10 Np (c)
electronvolt (d) eV 1 eV = 1.602 18 x 10-19 J, approximately
unified atomic mass unit (e) u 1 u = 1.660 54 x 10-27 kg, approximately
astronomical unit (f) ua 1 ua = 1.495 98 x 1011 m, approximately
(a) In many countries, this unit is called "tonne.''
(b) The bel is most commonly used with the SI prefix deci: 1 dB = 0.1 B.
(c) Although the neper is coherent with SI units and is accepted by the CIPM, it has not been adopted by the General Conference on Weights and Measures (CGPM, Conférence Générale des Poids et Mesures) and is thus not an SI unit.
(d) The electronvolt is the kinetic energy acquired by an electron passing through a potential difference of 1 V in vacuum. The value must be obtained by experiment, and is therefore not known exactly.
(e) The unified atomic mass unit is equal to 1/12 of the mass of an unbound atom of the nuclide 12C, at rest and in its ground state. The value must be obtained by experiment, and is therefore not known exactly.
(f) The astronomical unit is a unit of length. Its value is such that, when used to describe the motion of bodies in the solar system, the heliocentric gravitation constant is (0.017 202 098 95)2 ua3·d-2. The value must be obtained by experiment, and is therefore not known exactly.

There is no disagrement as to the definition of a db. All your definitions refer to it as a "unit" measure which I have always maintained. and many of you have not you .....that it is the log of a ratio...which we agree, and that once evaluated it represents a defined ratio which I have stipulated...is often the case.
You keep saying what a decibel is "used for" I keep agreeing: comparing two quantities and that is a primary use in science....there is agreement....because hearing, as your definition says, is a log function, that's what Bell had in mind.
I'll end, with a shovel may be used to dig a hole......but a shovel is not a hole....the disagreement we have is the same that math majors have with field majors all the time; we use strick definitions....you use applied definitions...your definition works for you, mine is not incorrect as yours is not; because as you want to use my definition in your context it becomes confusing to a field major....if you look at math texts; physical science texts as well as your own, you might not only appeciate the difference but celebrate it. By the way, you didn't appreciate me injecting humor into the discussion, no more than I appreciate some of you injecting vulgarity. I apologize for the both of us.
.Have a nice day !

Well there clearly is a disagreement. You claimed the following things:

db IS a unit measure in the same vain as a foot and meter are unit measures.

db measures sound level as a unit measure, miles measure distance as a unit measure, watts measure electricity as a unit measure etc. and some unit measures are ratios; and some are not..........

Those claims are mistaken.

I have explained in detail why your understanding of the decibel is mistaken, and I have cited several sources which substantiate my explanations.

As for definitions, you are the one being loose with your words. I've tried to be fairly clear, but you keep pretending that dB has dimensions

I don't know how you can claim that your position is correct, because it is not. dB does not have dimensions, and dB does NOT refer to sound pressure level. dB can refer to anything. The question is not a math question at all, so I don't see how mathematical texts have any relevance. The question of what a dB is, is not defined by mathematics. If you are going to assert that dB is some kind of scientific unit with dimensions akin to measurements like length, time, etc, we must consult scientific consensus about what these things are. Clearly, your claims that dB is some kind of measurement similar to SI units is mistaken. Mathematics has no bearing on this determination. Mathematics is not involved in the definition of SI base units or their derivatives.

If you are going to continue to maintain that dB is in any way comparable to base units like meters, kilograms, seconds, or their derivatives (such as meters per second) then you will continue to be mistaken. dB is not in any way analogous to these units. dB is completely absent from the SI base units or their derived units.

dB is completely absent from the SI base units or their derived units.

Wrong. look at y post right above yours. straight from SI. this is my last post i'm tired of dealing with a bunch of dumb asses.

Have a nice day !

in your own quote "It is a Unit". not all units of measure are SI but some outside of SI are APPROVED

"decibel
One-tenth of a bel. Symbol, dB, but see below. (Though the decibel is not an SI unit, the SI convention that a letter representing a person's name in a symbol is capitalized is observed with this unit. The B is for Alexander Graham Bell.) A unit used in electrical engineering and acoustics to express on a logarithmic scale the ratio between two values with the same dimensions"


http://physics.nist.gov/cuu/Units/outside.html
Units outside the SI

Certain units are not part of the International System of Units, that is, they are outside the SI, but are important and widely used. Consistent with the recommendations of the International Committee for Weights and Measures (CIPM, Comité International des Poids et Mesures), the units in this category that are accepted for use with the SI are given in Table 6.

--------------------------------------------------------------------------------
Table 6. Units outside the SI that are accepted for use with the SI
--------------------------------------------------------------------------------

Name Symbol Value in SI units
minute (time) min 1 min = 60 s
hour h 1 h = 60 min = 3600 s
day d 1 d = 24 h = 86 400 s
degree (angle) ° 1° = ( /180) rad
minute (angle) 1 = (1/60)° = (/10 800) rad
second (angle) 1 = (1/60) = (/648 000) rad
liter L 1 L = 1 dm3 = 10-3 m3
metric ton (a) t 1 t = 103 kg
neper Np 1 Np = 1
bel (b) B 1 B = (1/2) ln 10 Np (c)
electronvolt (d) eV 1 eV = 1.602 18 x 10-19 J, approximately
unified atomic mass unit (e) u 1 u = 1.660 54 x 10-27 kg, approximately
astronomical unit (f) ua 1 ua = 1.495 98 x 1011 m, approximately
(a) In many countries, this unit is called "tonne.''
(b) The bel is most commonly used with the SI prefix deci: 1 dB = 0.1 B.
(c) Although the neper is coherent with SI units and is accepted by the CIPM, it has not been adopted by the General Conference on Weights and Measures (CGPM, Conférence Générale des Poids et Mesures) and is thus not an SI unit.
(d) The electronvolt is the kinetic energy acquired by an electron passing through a potential difference of 1 V in vacuum. The value must be obtained by experiment, and is therefore not known exactly.
(e) The unified atomic mass unit is equal to 1/12 of the mass of an unbound atom of the nuclide 12C, at rest and in its ground state. The value must be obtained by experiment, and is therefore not known exactly.
(f) The astronomical unit is a unit of length. Its value is such that, when used to describe the motion of bodies in the solar system, the heliocentric gravitation constant is (0.017 202 098 95)2 ua3·d-2. The value must be obtained by experiment, and is therefore not known exactly.

Read the thread.

It's all explained.

I'm not going to be everyone's personal english teacher in addition to their science teacher.

For all of you who think that a deciBel (or a Bel) is a unit with dimensions, please explain to all of us what a decibel is. What are its dimensions expressed in SI units? What IS a decibel, fundamentally? Can you explain these things and cite any scientific references that explain this? I mean, sh*t or get off the pot.

The decibel has been explained, but for some reason you think that the earth is flat and that the decibel is something other than what every scientist or engineer who uses decibels thinks they are. What you posted has nothing to do with your claims. Decibels is not a quantity or a measurement of some dimension. Apparently some people think that decibels ARE actual things that can be measured, as if there is some dimension that is a decibel out there that we can go count in the manner that there is some quantity of mass out there that qe can quantify with kilograms. It's simply not the case.

Wrong. look at y post right above yours. straight from SI. this is my last post i'm tired of dealing with a bunch of dumb asses.

Are you joking?

This is directly from BIPM:
http://www.bipm.org/en/si/si_brochure/chapter4/4-1.html

Non-SI units accepted for use with the SI, and units based on fundamental constants

Table 8 also gives the units of logarithmic ratio quantities, the neper, bel, and decibel. These are dimensionless units that are somewhat different in their nature from other dimensionless units, and some scientists consider that they should not even be called units. They are used to convey information on the nature of the logarithmic ratio quantity concerned. The neper, Np, is used to express the values of quantities whose numerical values are based on the use of the neperian (or natural) logarithm, ln = loge. The bel and the decibel, B and dB, where 1 dB = (1/10) B, are used to express the values of logarithmic ratio quantities whose numerical values are based on the decadic logarithm, lg = log10. The way in which these units are interpreted is described in footnotes (g) and (h) of Table 8. The numerical values of these units are rarely required. The units neper, bel, and decibel have been accepted by the CIPM for use with the International System, but are not considered as SI units.

The SI prefixes are used with two of the units in Table 8, namely, with the bar (e.g. millibar, mbar), and with the bel, specifically for the decibel, dB. The decibel is listed explicitly in the table because the bel is rarely used without the prefix.



End of story. The decibel is NOT an SI unit. You CANNOT express a decibel in SI units all by itself. By itself, a decibel has no meaning. I feel like I'm pulling teeth with a bunch of three year olds who think santa claus exists.

Here is an example:

My unit here is the moron. I have made this unit up for the sake of this example, but there are discrete quantities of individual objects which we may call "morons."

There were, at some chosen point, originally 129 morons measured, but there are now 437 morons measured.

I can express the relationship between this change in the number of morons in many ways.

For instance, I could express it as a difference(or delta), in that there was a change of +308 morons (437-129=308)

Or I could express it as a percentage increase: 100x (437/129) = ~338.8% increase in morons.

Or I could express it in decibels: 10 log (437/129) = ~5.3 dB increase in morons.

Do you see how decibels can be used to represent various measurements? But that decibels themselves are not a quantity or dimension OF something particular (such as quantities of mass, time, distance, "morons," etc).

Decibels can thus be used to deal with logarithmic quantities extremely well in intuitive ways. This may not be particularly useful in dealing with things that change linearly or have linear relationships, but as one may experiementally deduce that the number of morons in the general population appears to be growing exponentially, it may be useful to express quantities of "morons" using decibels.

I really don't want you to blow a gasket..so we'll make one last attempt to agree..
Here goes....first, my focus was never on what a decibel was with respect to other functions, just a caution in its' interpretation...I did not want to imply that a 3 ft was like 5 dB dimensionally. Only that a foot and a dB were units....If I ask a person what is the unit measure in 3 ft, they respond: 1 foot,
If I ask them what it measures; they would say a foot.
If I ask them what the unit is in 5 dB, they would say 1 dB.
If I ask them what it measures; they should say "nothing"
dB are non dimensional and have no measure.....no problem
But, if I use the dB exponential function as a model to describe the relationship between two variables, then I may describe it as a measure in dB, and only with respect to the two values. The two values are dimensional, and I could use them to obtain the measure in dB which is not.....dimensional analysis to obtain a unit....the dB, which I hope is a unit of measure w/o dimension...If not
you're beyond me.....
Have a good day .

I really don't want you to blow a gasket..so we'll make one last attempt to agree..
Here goes....first, my focus was never on what a decibel was with respect to other functions, just a caution in its' interpretation...I did not want to imply that a 3 ft was like 5 dB dimensionally.

Except that not only did you imply that to be the case, you stated outright that this was the case. I am glad to see that you have corrected your position about this.

Only that a foot and a dB were units....If I ask a person what is the unit measure in 3 ft, they respond: 1 foot, If I ask them what it measures; they would say a foot.

Yes, they could also say that the dimension of this unit is distance, because that is what the unit "foot" quantifies."


If I ask them what the unit is in 5 dB, they would say 1 dB.
If I ask them what it measures; they should say "nothing"
dB are non dimensional and have no measure.....no problem

Correct. I am glad you have come to understand this. However, one could describe what we are comparing. For instance, returning to something that is commonly encountered, we could quantify Sound Pressure Level using decibels. If we were doing so, in that particular instance, the person answering might say "sound pressure level" or provide you with units of pressure such as the pascal.


But, if I use the dB exponential function as a model to describe the relationship between two variables, then I may describe it as a measure in dB, and only with respect to the two values. The two values are dimensional, and I could use them to obtain the measure in dB which is not.....

That is correct.

I want at least an A- !!!!!

Sorry, but those CD do not sound good at -25 db. In fact they don't sound good at any db.

Ed


:confused: Wow. What a *#$@. :(

In SI, the decimal submultiplier prefix meaning 1/10. BTW i dont work for weights and measures, the ruling department on units of measure. i'm just suppling their info for you.

Targus if you are so smart about everything why dont you go and start your own weight and measures company. i'm sure you could get chris w to go with you.


Dont be so childish.

You should understand what you're quoting or linking to, prior to posting it.
You look foolish.

[QUOTE=
Correct. I am glad you have come to understand this. However, one could describe what we are comparing. For instance, returning to something that is commonly encountered, we could quantify Sound Pressure Level using decibels. If we were doing so, in that particular instance, the person answering might say "sound pressure level" or provide you with units of pressure such as the pascal.
That is correct.[/QUOTE]

Just a final point.....once I define a dB with respect to two variables, psi, or kPa, or what ever pressure variables you want to use and use DA to define it as a location on the graph of the dB log function, each and every dB on the continuous graph over the interval 0 to infinity is defined, has a location which is defined, has a derivative( it exists ), which is then slope of the tangent at that point(instantaneous rate of change)......all that is true as we can't have a derivative at an undefined point or point of discontinuity...and according to DA (dimensional analysis) if we define a dimensionless variable in terms of two variables that have dimension, that variable dB, now has dimension with respect to those variables. It defines a unique location, it must have now have dimension (coordinates) that define its location.
So I believe "fico" was correct, that a dB is a unit measure under defined constraints, and that, as long as I prefaced my remarks with an implied "analysis"as we discussed relative sound level (which I hope did)...then, 86 dB for example, and every dB from 0 to infin. defines a unique point, and therefore can be referred to as a unit measure (more correctly adding with respect to the two variables representing pressure; that darn ratio again that everyone refers to)
So...if I DID NOT make myself clear enough that I was talking about sound level....you are correct, dB's are dimensionless units, unlike ft., otherwise they can both be referred to as unit measure under defined conditions.
Albert would be happy to know that everyone is correct from their point of view...

Just a final point.....You are inviting another dissertation on the laws of physics by you know who :)

:confused: Wow. What a *#$@. :(
:confused:

Ed

Ed,

I re-read your original post in this thread and it's spot on. I don't know what the eff cyberbri is suggesting?..But your comment and direct reference to "incompetence and ignorance" rampant in the CD recording industry regarding dynamic range compression... is "FACT"!

You are inviting another dissertation on the laws of physics by you know who :)

Oooops !!...spoke w/o thinking again .

Just a final point.....once I define a dB with respect to two variables, psi, or kPa, or what ever pressure variables you want to use and use DA to define it as a location on the graph of the dB log function, each and every dB on the continuous graph over the interval 0 to infinity is defined, has a location which is defined, has a derivative( it exists ), which is then slope of the tangent at that point(instantaneous rate of change)......all that is true as we can't have a derivative at an undefined point or point of discontinuity...and according to DA (dimensional analysis) if we define a dimensionless variable in terms of two variables that have dimension, that variable dB, now has dimension with respect to those variables. It defines a unique location, it must have now have dimension (coordinates) that define its location.
So I believe "fico" was correct, that a dB is a unit measure under defined constraints, and that, as long as I prefaced my remarks with an implied "analysis"as we discussed relative sound level (which I hope did)...then, 86 dB for example, and every dB from 0 to infin. defines a unique point, and therefore can be referred to as a unit measure (more correctly adding with respect to the two variables representing pressure; that darn ratio again that everyone refers to)
So...if I DID NOT make myself clear enough that I was talking about sound level....you are correct, dB's are dimensionless units, unlike ft., otherwise they can both be referred to as unit measure under defined conditions.
Albert would be happy to know that everyone is correct from their point of view...

No, Fico was incorrect. You, however, get it now. Although I don't see how derivatives are at all pertinent.

No, Fico was incorrect. You, however, get it now. Although I don't see how derivatives are at all pertinent.

Redundancy.

Well, for DVDs and such there is a reference which if you calibrate to to align with zero, you are then -x db from reference, or at reference or x dbs above reference.

Unless you've calibrated reference level to be zero in your system, it doesn't really matter. And it doesn't matter for music CDs etc.





That is a bunch of THX crapolla. You can always tell a THX follower just by what they write!

As part of their specification, THX units require the THX unit to have the ability to calibrate 0-dB as Dolby Reference Level output when measured at the listening position. If you use the receivers test tones to calibrate, then you get it right (0-dB = Dolby Reference Level). If you use any of those test DVD's (Dialnorm -27), then you are off by -4 dB (Dialnorm offset).

For non-THX units (like my Sony STAR-DA4ES), 0-dB means the preamp section is set to maximum volume (0-dB is maximum preamp volume setting). For example, calibrated Dolby Reference Level output when measured at the listening position in my room is -25 dB on my non-THX Sony display.

On the THX unit (if calibrated properly), then setting the volume at say -10 dB means that you have set the volume at 10 dB below Dolby Reference Level. For the non-THX Sony display, -35 dB is 10 dB below Dolby Reference Level.

In addition, neither unit is calibrated for DTS "Reference Level".

In general, CD's have no calibrated "Reference Level" so the number on the display means nothing much at all in absolute terms. It is just a number!





In any case, set the volume dial where things are appropriate for you. And don't listen too loud or you *will* damage your hearing over time.


True, but for DVD playback you should know how loud (AKA volume setting) Dolby "Reference Level" is on your system regardless of the use of the THX 0-dB scale, the Sony type preamp level 0-dB scale, or the use of an absolute non dB scale.

Just for the record, you can assume that dB's on a receiver refer to the change in the relative voltage output of the unit. If you are lucky, then the dB's also correspond to dB in SPL's that you get out of your speakers.

In my system, the receiver's display does correspond to relative dB SPL's. If I turn the volume down by 5 dB, then my receiver's calibration tone when measured at the listening position is also reduced by 5 dB SPL C scale.

As part of their specification, THX units require the THX unit to have the ability to calibrate 0-dB as Dolby Reference Level output when measured at the listening position. If you use the receivers test tones to calibrate, then you get it right (0-dB = Dolby Reference Level). If you use any of those test DVD's (Dialnorm -27), then you are off by -4 dB (Dialnorm offset).

Not quite following you here J.

If the calibration DVD has a Dialnorm correction/compensation, shouldn't I see that on the display of my pre/pro? I see the Dialnorm compensation displayed if a movie has it...

your comment and direct reference to "incompetence and ignorance" rampant in the CD recording industry regarding dynamic range compression... is "FACT"!

I would say that the recording industry quite knowingly and willingly over-compresses and over-processes sound recordings, because 99% of the market (from FM listeners to car listeners to iPod listeners) do not have listening places that can deal with any kind of dynamics, and those limited pieces of equipment will not compress on their own.

The ideal production chain would be to ship uncompressed source material, and have your car/ipod/radio/built-in TV speaker fed by a compressor tuned to the output.

The recording industry is not incompetent -- they are very competent at serving the biggest, most profitable consumer base, at the expense of the fringe where we both probably live.

The recording industry is not incompetent -- they are very competent at serving the biggest, most profitable consumer base, at the expense of the fringe where we both probably live.It's a pretty sad situation if only the fringe are asking for decent recordings.

But I believe that there is a whole new generation out there that has no idea of what good audio reproduction is because of the way things have evolved. If they had any inkling, then there'd be more demand for quality recordings.

Ed

The bottom line is that most people in here are refering to SPL when they say dB. Getting into the math is more likely to cause confusion even if it's well meant IMO.

That is a bunch of THX crapolla. You can always tell a THX follower just by what they write!



I recall now why you are on my ignore list. What I said there has nothing to do with THX at all.

Accusing me of being a THX follower is pretty hilarious. I have quite a few negative opinions about THX which are actually quite strong. Overall THX has done a lot of good, but I believe I've stated before that some of their ideas are borderline crackpot. Their ideas in the video domain are particularly bizarre, and I think on several occasions(relating to their Optimode system) I suggested that perhaps their video engineers were on drugs. I suppose that makes me a "THX follower?"

More power to ya buddy.

The bottom line is that most people in here are refering to SPL when they say dB. Getting into the math is more likely to cause confusion even if it's well meant IMO.

What about all the times we discuss crossover slopes, or amp gains, etc?