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Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 17

post #481 of 9620
Jerry, could you edit your post above? You've mistyped Hz instead of db numerous times which might confuse the REW fledglings.

I'd help out, but I'm posting off my phone for the next few days, which makes it a pain.


Max

Gear mentioned in this thread:

post #482 of 9620
Quote:
Originally Posted by djbluemax1 View Post

Jerry, could you edit your post above? You've mistyped Hz instead of db numerous times which might confuse the REW fledglings.

I'd help out, but I'm posting off my phone for the next few days, which makes it a pain.


Max

 

Of course, I do that a lot, even though I proof-read my work before posting.  It must be a mental block.  I have edited the original post, and think I have corrected all (or most of) the typos.  wink.gif

 

Thanks!

post #483 of 9620
Quote:
Originally Posted by AustinJerry View Post

Clipping indicates the mic level is too high.  Suggestions:  Lower the microphone volume in Windows audio (I use 60 as the volume setting).  Then re-calibrate the mic in REW, adjusting AVR volume to reach 80dB reading on the SPL held next to the mic, and then keying in 80dB in the calibration setting.  Then the measurement sweep should not cause clipping.

Got it, thanks Jerry. Now to learn how to perform a waterfall graph smile.gif.
post #484 of 9620
Quote:
Originally Posted by AustinJerry View Post

So, what are the take-aways?

 

1.  Always set the lower limit on the vertial axis equal to the noise threshold of your listening room (use 40dB if you don't know).

2.  Set the horizontal axis to the frequency range you want to examine, 20Hz-200Hz in my examples.  (Note:  many experts say to ignore the frequencies below 40Hz, because there are very few treatments that can fix resonances in this range.)

3.  Adjust the time axis, starting at 300ms, until you have a meaningful indicator of where the resonance issues are.

 

Of course, the interesting discussion will be, what value of the time axis represents a "good" decay time, and what values show issues that need to be resolved.  In other words, if everything has decayed in a shorter time than 600ms, is that "good enough"? A second interesting discussion will be, what types of room treatments address issues at specific frequencies, e.g. what to use for a 40Hz resonance vs. a 90 Hz resonance--the answer is likely to be different.

 

Tip:  How do I measure the noise threshold of my listening room?  Answer:  In REW, after you have performed the microphone calibration (Step 5 in the Guide), click the red button in the SPL Meter tool.  The meter will display the ambient noise level in the room.  Assuming you have gone to the effort to make sure it is as quiet as possible, the meter will display your room's noise floor.

 

 

 

Jerry - another brilliant and incredibly useful post. This is just the sort of thing we need in the User Guide IMO. Thank you for the time and effort you are putting into this. I am sure I speak for everyone when I say this.

post #485 of 9620
Quote:
Originally Posted by AustinJerry View Post

Quote:
Originally Posted by djbluemax1 View Post

Jerry, could you edit your post above? You've mistyped Hz instead of db numerous times which might confuse the REW fledglings.


I'd help out, but I'm posting off my phone for the next few days, which makes it a pain.



Max

Of course, I do that a lot, even though I proof-read my work before posting.  It must be a mental block.  I have edited the original post, and think I have corrected all (or most of) the typos.  wink.gif

Thanks!
Looks great!


Max
post #486 of 9620
Quote:
Originally Posted by kbarnes701 View Post

Quote:
Originally Posted by AustinJerry View Post

So, what are the take-aways?

1.  Always set the lower limit on the vertial axis equal to the noise threshold of your listening room (use 40dB if you don't know).
2.  Set the horizontal axis to the frequency range you want to examine, 20Hz-200Hz in my examples.  (Note:  many experts say to ignore the frequencies below 40Hz, because there are very few treatments that can fix resonances in this range.)
3.  Adjust the time axis, starting at 300ms, until you have a meaningful indicator of where the resonance issues are.

Of course, the interesting discussion will be, what value of the time axis represents a "good" decay time, and what values show issues that need to be resolved.  In other words, if everything has decayed in a shorter time than 600ms, is that "good enough"? A second interesting discussion will be, what types of room treatments address issues at specific frequencies, e.g. what to use for a 40Hz resonance vs. a 90 Hz resonance--the answer is likely to be different.

Tip:  How do I measure the noise threshold of my listening room?  Answer:  In REW, after you have performed the microphone calibration (Step 5 in the Guide), click the red button in the SPL Meter tool.  The meter will display the ambient noise level in the room.  Assuming you have gone to the effort to make sure it is as quiet as possible, the meter will display your room's noise floor.


Jerry - another brilliant and incredibly useful post. This is just the sort of thing we need in the User Guide IMO. Thank you for the time and effort you are putting into this. I am sure I speak for everyone when I say this.
Since this topic has already popped up, I figured I'd comment.

As far as the time range for waterfalls, there are 2 approaches:
1) as Jerry states, increase the decay time setting till you can see the majority of the peaks fall to the noise floor (set at 40db or your individually measured noise floor). This is great for folks curious to see what their room is doing and can help ID modal ringing.

2) set the decay range to 300ms as the goal is to have everything above ~40Hz decay in under 300ms (or by about 200-250ms in ideal conditions).

It's not only important to have the frequencies decay by a certain time, it's also important that the frequency range decays at similar rates over the entire range.

For example, if the octave from 60-120Hz decays much slower than 30-60Hz and 120+Hz, that octave will dominate what is heard. It will also mask/blur everything else.

Because it's harder to damp/absorb bass frequencies than mids and highs, the type and amount of absorption used to control the bass may inadvertently absorb too much of the higher octaves, resulting in drastically shorter high frequency decay rates, which will produce tight bass, but a 'dead' sounding room.

How much treatment is good and how much is too much is something we'll get to later I'm sure, but to get back to the specific issue, if it takes more than 600ms for the bass to decay into your noise floor, you seriously need bass traps anyway, and showing a waterfall to 1000ms is unnecessary, except to show just HOW badly bass traps are needed.

BTW, when folks begin producing waterfalls, they'll see just how powerful XT32 is for reigning in bass ringing, but of course, the better the situation prior to running Audyssey, the easier it is for Audyssey to do its thing and the better the outcome.


Max
post #487 of 9620
^ Good stuff, Max. I wish I had more of this knowledge when I started treating my room. If it weren't so much trouble, I would remove all of the treatments, take some measurements, and begin adding back the treatments one at a time to see which are actually effective.

Edit: Unfortunately, I may have to do this. If our exercise here points to needing more treatments, I don't have any more spots to place them. Something will have to go.
post #488 of 9620
I would like to give props to all the people who have contributed to the making of this thread. Everyday for the last two weeks I've been reading this thread, it's a bit addictive! Its basically like going back to college and taking a REW elective course tongue.gif.
Thanks Jerry and Max for the wealth of information on waterfall and decay.
post #489 of 9620
Thread Starter 
Quote:
Originally Posted by batpig View Post

Quote:
Originally Posted by AustinJerry View Post

I am the messenger here, so there is no cause to get upset. 

Not at all upset with you. Just annoyed that this is getting more complicated than I was led to believe. I went from having a simple answer that no additional equipment would be needed beyond the USB mic, and I could use standard analog audio output to generate the test tones, to your response, thus it feels like it's going backwards.

As I understood it, the audio output portion (HDMI vs. whatever) was secondary; the initial impetus was about the INPUT portion, i.e. the USB mic obviating the need for additional gear (external soundcard, phantom power, etc). The HDMI output aspect was secondary "gravy" for people who were fascinated by the idea of being able to ping each channel individually. But when jevansoh originally introduced the topic it was not limited in scope to the HDMI output option; the specific form of signal generation wasn't really relevant. I don't know at what point the two merged but when it was initially discussed in the Audyssey thread the two were NOT linked.

Quote:
I don't know where you got the idea that you would be able to use your laptop's audio if your laptop has no HDMI port.

Not sure, but maybe it was the part where Jason explicitly said that was the case when this was initially being pitched in the Audyssey thread?
Quote:
Originally Posted by jevansoh View Post

Here's some more info for everyone.

While it is true that REW generates the signal internally, meaning you will have to hook your computer/laptop up to any available stereo input on your AVR, you will not need to use an external CD/DVD Player and CD/(DVD??) like you do with Omnimic/RTZ so that pretty much cancels each other out as far as I'm concerned.

There are no other "black boxes" needed. You will NOT need a full duplex sound card because you aren't using the sound card's mic input and speaker/line output at the same time, as you'll be using the USB Mic. So the built-in sound card that every PC/Laptop has works fine. (Using it this way myself on a cheap laptop)

Yes, the output/jack on the sound card is 1/8" stereo mini and Yes, the input on the AVR is RCA, but that is taken care of by a $3.00 1/8" to RCA Splitter/Y-Adapter that I bet most of you already have.
Quote:
Originally Posted by jevansoh View Post

You will NOT need an "external" sound card. I'm SURE your PC/Laptop has a sound card and the one that is built-in is more than adequate if manufactured in the last 10 years or so. Promise! (My business is computer hardware/software, sales and service, in business since 1994, so I'm sure of this)

Yes, the front AUX is exactly what I use. If you want "easy" (actually, every method is very easy, but this is the long-term/in-use tried and true method) and only care about the front 3 channels as far as testing goes, then you can use a simple RCA cable, and 25' or so is fine, but I wouldn't go more than 50' max, and stay as close to 25' as possible.

Monoprice makes great ones and you can do the same for even less. All they do is use standard RG-6 Sat/CATV cable and put some RCA plugs on the end. I make my own for even less, but if you don't want to fool with it and don't need custom lengths, their prices cannot be beat.

You'll simply plug the mic in to your PC/Laptop (Up to 15' standard USB extension cable can be used and if you need longer than that, Monoprice again has wonderful and cheap options for amplified USB cables for much longer lengths) and then from the sound card in the same computer you'll run an RCA cable back into your pre-pro's AUX input.

That's it!
Quote:
Originally Posted by jevansoh View Post

No No no... wink.gif NOT $200. You do not need any external sound card if using a USB Mic because you no longer need full duplex capabilities since you won't be using the sound card for "input" (that will be the USB Mic now) at the same time as "output." The output is all you'll be using on the sound card and I haven't seen a PC/Laptop since about 1997 that doesn't have a built-in sound card, so I'm sure you don't have to purchase anything but the Mic which is less than $100. smile.gif

--J
Quote:
Originally Posted by jevansoh View Post

Quote:
Originally Posted by kbarnes701 View Post

When you say the 'sound card in the same computer' this would be the audio out connection I assume? This seems to be limited on my machine (from memory) to the headphone out socket - is that what you mean?

Yes, the headphone out is fine. You'll simply plug an RCA cable from that (may need a 1/8" to RCA adapter for a buck or so at Monoprice) into the front AUX on your Onkyo, then plug the Mic into a USB port on the same laptop and that's it! If doing it this way, you won't even need to fool with the ASIO driver because that's just for HDMI and if you want all 8 channels.


So, yeah, I think that was a reasonable inference on my part.

Quote:
This thread was established to specifically leverage a new capability in REW 5.0 beta 10 that added support for laptops with HDMI and USB mics. AFAIK, nothing has changed with regards to how to do a legacy connection.


Well I guess you missed this exchange.
It's disappointing to me that the scope has narrowed from the original introduction in the Audyssey thread such that it's now exclusionary towards those who don't have the HDMI output option.

Again, I don't understand why the OUTPUT aspect has to be linked with the input side. It's almost certain that I am misunderstanding something, but I though the biggest revelation of the process was the support for PnP (or almost) USB mics making the intro to REW much more accessible. What does it matter how the funny test tone sounds gets from the laptop to the speakers? If the speakers make noise, can't you measure it?

Quote:
If you read the REW documentation, it states: "Equipment Needed: A soundcard (internal or external) with line inputs and outputs. Note that most PC and laptop mic inputs are NOT suitable and should not be used (they have too much gain and most suffer from high noise levels and limited bandwidth)."

(snip)

A microphone input (mic-in) on a soundcard is not suitable (many laptops only have mic-in).

OK, that's all warning about the mic INPUT portion. That's the part that is now obviated by the USB mic (as I understood it). All I'm talking about is the sound OUTPUT, the signal generation portion.

I'm not trying to be a dick, and I truly don't understand enough about the topic to know where I'm going astray, but I feel like what you are telling me does not jive with what was originally discussed during the genesis of this idea in the Audyssey thread.

I am obviously a few days behind. Catching up right now.

It's possible I'll find through further reading that this has already been cleared up.

However, I want to make sure it comes from the horses mouth, so to speak.

BP, you are correct. Everything I stated before is correct. There are no changes.

Jerry was also correct, however, in referring to Legacy setups.

So, to break it down once more...

IF, you are using a mic, mic pre-amp, and connecting both to the input of your laptop/PC and using that same device (sound card) to output (not HDMI) then you "might" need an external sound card. Technically, what you need is a "Full Duplex" Sound Card. I happen to use a 4 year old Dell Laptop for REW measurements and its built in sound card is full duplex so even using a RatShack SPL meter or other mic/mic preamp combo, I don't need an external sound card. If you have an older laptop or PC without a full-duplex sound card and are using an analog (not USB) mic, then you need an external sound card, too.

IF, you are purchasing a new UMM-6 or UMIK-1 USB Mic then you do NOT need an external sound card. It doesn't matter if the sound card that's built into your Laptop or PC is full duplex or not, because you aren't going to be using the input and output at the same time. In fact, you aren't using the input at all. Only the output. So ANY audio out connection will work from a Laptop/PC using a USB Mic.

This has NOTHING to do with whether or not you are using HDMI as you could still use HDMI output and an old fashioned mic and mic pre-amp as the input.

Hope this clears things up, and again, sorry if it has already been cleared up but I didn't want to take that chance and have to find this post again, especially since it seemed tension was high regarding this misunderstanding.

In other words, BP, you're fine and your original thinking (in your case) is correct.

Have fun,

--J
post #490 of 9620
Thread Starter 
Quote:
Originally Posted by kbarnes701 View Post

Quote:
Originally Posted by JimP View Post

Quote:
Originally Posted by AustinJerry View Post

The sound card calibration instructions were intended for those of us who are using the Audyssey mic, plugged into the mic input on the laptop. I believe we have said several times that the guide will need to be revised once we have USB mics available for testing. Whether or not a sound card calibration will be required or not I cannot say at this time.
Jerry,


That may be so, but in post 453 you were replying to someone who had stated that he'd be using a usb mic.


On the bright side, we're making progress on some of these finer points. smile.gif

Yes we are. I am hoping Jason is working on a step-by-step guide to using the mic once it arrives (unless you are taking on this mantle, Jerry?). From plugging in (with REW all set up to go as per Jerry's guide) to taking the first set of measurements, to generating some graphs, and to interpreting the results, and suggestions as to how to improve on them...

I'd like to know which speakers to measure, which combinations of speaker to measure, how many measurement positions to use, etc etc - and then take it from there.

Hi Keith,

I am not the best person to create the document itself simply due to time which I sure wish there was more of.

However, as soon as the USB Mics start shipping and the speculation stops (re connections, getting REW setup, etc) and the fun can begin I plan to very actively support and teach exactly what should be measured, why, and how to interpret the results including what can be done to improve them.

I am hoping through those responses and discussions either you or Jerry or possibly a collaborative effort from many users will be able to produce a nicely detailed document so future readers don't have to go through the same growing pains/learning curve.

Also, to be clear on the last topic, I haven't jumped in on a few things because in a lot of ways all of you have been "right" and none have been explicitly wrong.

The problem is, in many topics the answer "depends" and unfortunately there are lots of different types of setups, mics, USB mics, laptops, with/without external sound cards, using HDMI, not using HDMI, etc.

It seems that since there is a different answer for each person/setup it would only confuse things more if the post came directly from me replying to a particular user with his/her unique setup regarding cabling, mics, etc.

So I feel we need a document or post detailing the type of connections, cabling, and hardware needed for each "type" of setup.

However, the more documents we have, FAQ's we create, etc, the more confusing and troublesome the "answers" can become (re simply finding them) and so maybe it's best to simply flush out each Q&A on the thread, per user, each time it comes up, until actual trends start occurring and most everyone is on the same page and understands all the nuances.

Does that make sense? wink.gif

--J
post #491 of 9620
Thread Starter 
Quote:
Originally Posted by J_Palmer_Cass View Post

Quote:
Originally Posted by AustinJerry View Post

The sound card calibration instructions were intended for those of us who are using the Audyssey mic, plugged into the mic input on the laptop. I believe we have said several times that the guide will need to be revised once we have USB mics available for testing. Whether or not a sound card calibration will be required or not I cannot say at this time.



How do you do a soundcard calibration if you do not have a full duplex sound card?


Full duplex test:

http://www.ehow.com/how_7763496_check-sound-card-fullduplex.html

This is what I was talking about in my last post...

If you don't have a full duplex sound card and you use a USB mic, it doesn't matter, because you aren't using the input/output of the sound card at the same time, so you don't need full-duplex.

In fact, the ONLY time you need a Full Duplex sound card is if you are using an older, NON-USB Mic with a Mic Pre-Amp and connecting everything through the sound card, not using HDMI or USB - IE: The old way.

If you are using the old way for the mic but also use HDMI for the output then you still don't need a Full-Duplex sound card because, again, you aren't using the input and output on the sound card at the same time.

Also, if you aren't using the sound card's input, then of course you don't use a sound card calibration!! wink.gif

The reason I didn't mention that before is that I was trying to keep things simple and didn't know/feel at the time it should be mentioned what you do NOT need to do when using the new USB Mics. smile.gif

Anyway, assuming you are using a UMIK-1 MiniDSP Mic, you literally plug it in and don't worry about any other hardware or software for the "input" side of things.

As far as output goes, you can use the speaker/headphone out (analog) or you can use HDMI.

You don't need to worry about sound cards, calibrations, or anything else.

Hope this helps,

--J
post #492 of 9620
Thread Starter 
Quote:
Originally Posted by AustinJerry View Post

Quote:
Originally Posted by kbarnes701 View Post

I am hoping Jason is working on a step-by-step guide to using the mic once it arrives (unless you are taking on this mantle, Jerry?). From plugging in (with REW all set up to go as per Jerry's guide) to taking the first set of measurements, to generating some graphs, and to interpreting the results, and suggestions as to how to improve on them...

I was planning on amending the guide to reflect the differences when using the USB mic. Once we have mastered configuring the new hardware and we are generating meaningful measurements, we will graduate to the real purpose of the thread--analyzing the results and discussing remedial solutions. This part will differ for each set of measurements, and I doubt there is a single cookbook approach to fixing issue can be documented. Of course, we are hoping Jason re-joins the thread and shares his knowledge.

Don't worry, Jerry.

I haven't gone anywhere and I won't be leaving any time soon. biggrin.gif

There haven't been a lot of things over the last several days that by the time I read the posts (unfortunately only about once per day in the late evening, EST) aren't already cleared up, so I hate to reply to questions that have already been answered unless I feel people are still confused or there is an upset poster who is misunderstanding something.

Be sure that I read every word of every post though and when the mics come in (understand that I'm waiting, too!) I'm hoping the discussion can progress on to topics in which I have valuable and unique information to share.

You guys are doing fine without me for now. Again, if I see something that is simply wrong or I don't feel is cleared up well then I will follow up to do just that.

It's just that without having the mic and waiting like everyone else is doing, it'd be silly to progress too much when I know people cannot follow along. I ordered the UMM-6 mic, but to be able to offer tech support on the UMIK-1 mic I think I'm going to order that one, too, just to make sure I have everything that everyone else is using.

For anyone reading this, please do understand that although I cannot be as active on here as I'd like, I absolutely AM here and am not going anywhere any time soon.

I want to help, have a lot of information to share, and find all of this absolutely fascinating and enjoy teaching very much.

I promise there is a lot of valuable information to come, but now is simply not the time as I don't believe more than a handful of lucky people have been able to get their hands on these mics, myself included.

Soon, though..Soon.

--J
post #493 of 9620
Thread Starter 
Quote:
Originally Posted by LastButNotLeast View Post

re: soundcard calibration.
This is from my original experiences with REW:
Compaq Presario:




Mac mini:




Mobile Pre:




I will continue to use my RS meter and external card and Java, and will continue to wait eagerly for the rest of you to get your mics and start posting and discussing the resulting graphs.

In the meantime, here's my waterfall:




Hurry up, guys!
Michael

I wasn't going to reply to this simply because I don't want to get ahead of everyone else and start confusing people, but while we're waiting.... I couldn't resist. smile.gif

On first glance, that is the best waterfall I've ever seen and even better than mine, but...

Unfortunately, it is very deceiving and not true at all.

We need to see as close to 60db as possible and you are only showing a peak of about 87db to what looks like maybe 67db at the bottom end.

So that's only 20db. Re-Read the second post of this thread and reset your measurements using the "limits" section to show 90db down to 30db.

Then that waterfall won't look pretty at all, but will be honest, and will give us something to look at.

I eagerly await you reposting using those settings as it will prove a very valuable point to all and hopefully the same mistake won't happen again and we can all learn from it.

Plus, if there is no objection, I'd be happy to go into a little more analysis/detail once I can see what's truly going on when the limits are reset while we're all waiting on our mics.

Thanks,

--J
post #494 of 9620
Quote:
Originally Posted by jevansoh View Post

So I feel we need a document or post detailing the type of connections, cabling, and hardware needed for each "type" of setup.

However, the more documents we have, FAQ's we create, etc, the more confusing and troublesome the "answers" can become (re simply finding them) and so maybe it's best to simply flush out each Q&A on the thread, per user, each time it comes up, until actual trends start occurring and most everyone is on the same page and understands all the nuances.

 

+1 on the document detailing what's required depending on your setup.  While there does seem to be a lot of options, collecting each type of setup seems to be important enough to justify it.  Afterall, we're almost at 500 posts (not including the carryover from the Audyssey thread) and most of the discussion to this point has been dominated by "setup" (for understandable reasons of course).

 

I plan to order a USB mic but I know already that I don't have a laptop with HDMI.  I'm still not 100% certain I understand the cabling that is required with this type of setup?  I believe the question on the need for the Y splitter coming out of the laptop and going into the receiver via is clear now but is this and the USB mic all that is needed in terms of connections with this setup?  I would also suggest some links to specific cables/adapters for those less knowledgeable on these "bits" (as my friend's across the pond like to call them).

post #495 of 9620
Thread Starter 
Quote:
Originally Posted by AustinJerry View Post

Well, I'm not a whole lot further ahead than you are, Stuart, but I'll be glad to share my limited knowledge.

When a bass note is struck it will decay over time until it blends with the audio threshold of the listening room.  This gradual delay is called ringing or resonance.  The faster the sound decays, i.e. the lower the ringing, the tighter or more well-defined the bass will sound.  A long decay results in bloated, poorly-defined bass.

The waterfall measures the rate of decay in the listening room over time.  The vertical axis extends from the audio threshold of the listening room, typically around 40dB, to a value high enough to contain the peaks in the response measurement, normally around 90dB.  The horizontal axis shows the frequency response, normally in the range of 40Hz to the upper range of the bass that concerns you, say 100Hz-200Hz.  The third axis represents time, in mille-seconds.

So, looking at Michael's waterfall, we see he has selected 65-95dB on the vertical axis (which really should have a lower value of 40dB), and he is measuring from 20Hz-170Hz.  On the time axis, he has measured 0-300ms. 

My understanding is that the objective is to have all bass frequencies decay to below 40dB within the first 300-600ms.  Unfortunately, since Michael's waterfall only goes down to 65dB, he is not showing the noise threshold of 40dB.  I retract my earlier statement that the waterfall looks good--we actually don't have enough data.

Let's look at some examples (note that my time scale is 0-600ms--we'll come back to that in a moment):

First, a vertical axis of 65-95dB;




Now, 40-95dB:




And finally, 30-95dB:




The first waterfall shows that bass frequencies have fully decayed to 65dB within 100-150ms.  This waterfall is meaningless, since we want to show when the decay reaches 40dB.

The second waterfall is useful, because it shows that most, but not all, bass frequencies have decayed below 40dB by 600ms.  The exceptions are at 35Hz, 60Hz and 65Hz, all of which seem to be relatively minor.

The third waterfall is not so useful, because it shows decay to 30dB, which is 10dB lower than the noise threshold of the room.

Now let's see what varying the time axis does.  The graphs above had a 600ms time axis.  Let's go down to 300ms:




Big difference!  This shows that within 300ms, ALL of the bass frequencies are still present above 40dB.  This doesn't give us much information on where to focus our improvements.  Let's try 450ms now:




This is showing better information, but there are still quite a few frequencies not fully decayed by 450ms.   To arrive at a meaningful waterfall, we need to continue to increase the time delay until most, or all, of the frequencies are fully decayed.  If this occurs at a time delay of 600ms or lower, we are in reasonable shape.  If it exceeds 600ms, then those frequencies that are not fully decayed at 600ms should be the focus of our improvement effforts.

So, what are the take-aways?

1.  Always set the lower limit on the vertial axis equal to the noise threshold of your listening room (use 40dB if you don't know).
2.  Set the horizontal axis to the frequency range you want to examine, 20Hz-200Hz in my examples.  (Note:  many experts say to ignore the frequencies below 40Hz, because there are very few treatments that can fix resonances in this range.)
3.  Adjust the time axis, starting at 300ms, until you have a meaningful indicator of where the resonance issues are.

Of course, the interesting discussion will be, what value of the time axis represents a "good" decay time, and what values show issues that need to be resolved.  In other words, if everything has decayed in a shorter time than 600ms, is that "good enough"? A second interesting discussion will be, what types of room treatments address issues at specific frequencies, e.g. what to use for a 40Hz resonance vs. a 90 Hz resonance--the answer is likely to be different.

Tip:  How do I measure the noise threshold of my listening room?  Answer:  In REW, after you have performed the microphone calibration (Step 5 in the Guide), click the red button in the SPL Meter tool.  The meter will display the ambient noise level in the room.  Assuming you have gone to the effort to make sure it is as quiet as possible, the meter will display your room's noise floor.



Jerry, VERY GOOD POST!

I'm so jealous that you are able to be so much more eloquent and thorough in your posts than I have the time or patience for. Good job, my friend.

Now, everything you say is correct but I'd change "audio threshold" and "noise threshold" to the more common and correct term which is "Noise Floor."

Also, where you state it may not be necessary to show below 40hz, I 100% DISAGREE with that. Sorry.

Here's why. That will surely (in all but the absolute smallest of rooms) not show the first mode; the first Axial (length) mode to be exact.

This is very important because there are always artifacts at each doubling of frequency.

My room is 20' x 26' x 8' 8" and my first mode is 20hz. I have yet to conquer this mode and therefore have ringing that is still out to 800ms. (Was over 1.5 seconds before treatment) however, I've gotten ALL of my other modes to well below 500ms all the way down to my noise floor which is 37db in my quiet/dedicated room. (There is still a lot of room for improvement here, too)

Even with the level of treatment I have, I can still see the modes at 40hz, 60hz, and 120hz creep out a bit more than the frequencies between them. However, every time 20hz gets better (next project is targeted 20hz frequency helmholtz resonators) so do the other harmonic modes.

I wouldn't know where the problem began and what to truly "treat" if I didn't show below 40hz.

I recommend showing, on ALL waterfall graphs, for consistency sake, 15hz to 300hz.

That's how I display mine, how I've seen other pro acousticians display theirs, and what I'd appreciate seeing on this thread to be certain we're all looking at the full picture.

Along with a 60db vertical scale.

If, however, your noise floor is at 40db, then you cannot measure at 75db and get a true/accurate 60db scale, which is why I recommend getting measurements as close to 100db as you can stand. (Earplugs not optional if measuring at this level)

If you choose not to measure at 100db, at a MINIMUM, measure at 85db, so your peaks in an uncorrected bass response might be close to 100db without rattling your room and your teeth and taking any chance of damaging your equipment or ears, 85db is a good compromise.

Also, REW has built in noise filters and so it can accurately show to at least 5db (maybe more) below your in room recorded (with the SPL function) noise floor.

A good way to see how low you can set the lower limit without introducing the noise floor itself (which you don't want to do) is look at the waterfall and "in between" the mountains, where there are no modes, pay attention to one of those frequencies, then using the "limits" function, set the lower limit going lower and lower until you see "mountains" start to pop out of nowhere...That's your noise floor. Set the bottom limit a db or two above this point and from then on try to measure as close to 60db above that point as you can for the ultimate accuracy in your measurements and you'll have good accurate readings.

Again, great job on explaining things and even showing graphs!!

Thanks,

--J
post #496 of 9620
Quote:
Originally Posted by jevansoh View Post

So that's only 20db. Re-Read the second post of this thread and reset your measurements using the "limits" section to show 90db down to 30db.

Then that waterfall won't look pretty at all, but will be honest, and will give us something to look at.

I eagerly await you reposting using those settings as it will prove a very valuable point to all and hopefully the same mistake won't happen again and we can all learn from it.
 

Will do, but I was planning to wait until the new mics show up and we're all on the same page. Since it's a "legacy" system, it's a real PITA to set up, and not something you can leave sitting around a family room.

These mics are on a slow boat from China? wink.gif

Hurry up and let the fun begin!

Michael

post #497 of 9620
Quote:
Originally Posted by LastButNotLeast View Post

Will do, but I was planning to wait until the new mics show up and we're all on the same page. Since it's a "legacy" system, it's a real PITA to set up, and not something you can leave sitting around a family room.
These mics are on a slow boat from China? wink.gif
Hurry up and let the fun begin!
Michael

If you saved the .mdat file you can open it and apply any change you wish, ...if not,...we'll have to wait! cool.gif
post #498 of 9620
^^
Kudos to AustinJerry again for getting the ball rolling afer I asked a 'simple' question, and Jason for chiming in to supply added guidance about the measurement scale that one should use to get a waterfall that I hope takes this last month out of the realm of 'thought exercise' into something practical. Actually, I see the wisdom in why a waterfall is a more critical metric for the success of room correction that just FR, because it tells us more about the specific frequencies at which bass decay is outside of the 'acceptable range', and specifically which frequencies can be masked by the disparity in decay levels (i.e. under and over-emphasis). This redefines what "accurate bass" really is smile.gif beyond the conceptual level. And the need to be aware of the 'noise floor' is critical to help eliminate room characteristics, something you wouldn't know just from a FR measure. I'm eagerly awaiting my USB mic....

The practical issue, though, is that while I'd love to do 100 db measurements to rise above a hypothetical 40 db noise floor, I live in a condo, and it's hard enough to run 75 db tones let alone 100 db without ticking off the neighbors. I haven't tested it formally, but anecdotally a 'silent' measurement when I've done SPL format measurements with OmniMic shows more like 45-50 db noise floor than 40 (the background SPL you get without any of my audio channels getting a test tone). Imagine how much fun it will be to do 110 db tones to get a 60 db measurement above the floor...85's going to be stretching it, honestly.

Although due to a possible family expansion project, we might be moving in a year or so, and thus I'll have the joy of setting up an HT room from scratch...biggrin.gif That's where the learning may come in handiest. Easier to set up an HT room around your requirements than shoe-horning it into an existing room and furniture.
post #499 of 9620
Quote:
Originally Posted by LastButNotLeast View Post

Will do, but I was planning to wait until the new mics show up and we're all on the same page. Since it's a "legacy" system, it's a real PITA to set up, and not something you can leave sitting around a family room.

These mics are on a slow boat from China? wink.gif

Hurry up and let the fun begin!

Michael

 

So, if you had done a full range measurement, wouldn't it be possible to manipulate the data that you already measured?  Is this not possible now because you set limits prior to taking the measurements?  Just making sure I understand some of the nuances in REW prior to taking my own measurements.

 

EDIT:  I see Feri has basically asked the same question that I had.

post #500 of 9620
Quote:
Originally Posted by jevansoh View Post

Quote:
Originally Posted by kbarnes701 View Post

Quote:
Originally Posted by JimP View Post

Quote:
Originally Posted by AustinJerry View Post

The sound card calibration instructions were intended for those of us who are using the Audyssey mic, plugged into the mic input on the laptop. I believe we have said several times that the guide will need to be revised once we have USB mics available for testing. Whether or not a sound card calibration will be required or not I cannot say at this time.
Jerry,


That may be so, but in post 453 you were replying to someone who had stated that he'd be using a usb mic.


On the bright side, we're making progress on some of these finer points. smile.gif

Yes we are. I am hoping Jason is working on a step-by-step guide to using the mic once it arrives (unless you are taking on this mantle, Jerry?). From plugging in (with REW all set up to go as per Jerry's guide) to taking the first set of measurements, to generating some graphs, and to interpreting the results, and suggestions as to how to improve on them...

I'd like to know which speakers to measure, which combinations of speaker to measure, how many measurement positions to use, etc etc - and then take it from there.

Hi Keith,

I am not the best person to create the document itself simply due to time which I sure wish there was more of.

However, as soon as the USB Mics start shipping and the speculation stops (re connections, getting REW setup, etc) and the fun can begin I plan to very actively support and teach exactly what should be measured, why, and how to interpret the results including what can be done to improve them.

I am hoping through those responses and discussions either you or Jerry or possibly a collaborative effort from many users will be able to produce a nicely detailed document so future readers don't have to go through the same growing pains/learning curve.

Also, to be clear on the last topic, I haven't jumped in on a few things because in a lot of ways all of you have been "right" and none have been explicitly wrong.

The problem is, in many topics the answer "depends" and unfortunately there are lots of different types of setups, mics, USB mics, laptops, with/without external sound cards, using HDMI, not using HDMI, etc.

It seems that since there is a different answer for each person/setup it would only confuse things more if the post came directly from me replying to a particular user with his/her unique setup regarding cabling, mics, etc.

So I feel we need a document or post detailing the type of connections, cabling, and hardware needed for each "type" of setup.

However, the more documents we have, FAQ's we create, etc, the more confusing and troublesome the "answers" can become (re simply finding them) and so maybe it's best to simply flush out each Q&A on the thread, per user, each time it comes up, until actual trends start occurring and most everyone is on the same page and understands all the nuances.

Does that make sense? wink.gif

--J

 

Yes J it makes sense. I don't think we need to worry about documentation and FAQs *just* yet - when we all have our mics and really tart to learn, it will call come together IMO. I am happy to help write any documentation - writing comes easy to me. Also happy to help someone (like Jerry) who is many steps ahead of me to create documentation.

post #501 of 9620
Quote:
Originally Posted by jkasanic View Post

 

So, if you had done a full range measurement, wouldn't it be possible to manipulate the data that you already measured?  Is this not possible now because you set limits prior to taking the measurements?  Just making sure I understand some of the nuances in REW prior to taking my own measurements.

Probably, but it's old news anyway, so I'm just going to start over like everyone else.

Unfortunately, the room is an acoustic nightmare: 15 x 30, open on one side to the kitchen, fireplace on the other side, cathedral ceiling and two skylights.

Fortunately, it comes with a RESONABLY understanding wife. wink.gif

More fortunately, I'm not THAT picky, I just want to do the best I can with the new speakers that replaced my satelites and the second sub.

And have a little fun along the way, just like I did calibrating my RPCRT.

The guide being assembled here will be a GREAT help.

Thanks to all.

Michael

post #502 of 9620
Hi Guys,

The latest version of REW 5.1 Beta 13 is available for download from here.

Tip: Go to Help and make sure "Check for Updates on Startup" is checked so you don't loose on having the latest version. smile.gif
post #503 of 9620
Quote:
Originally Posted by mogorf View Post

Hi Guys,

The latest version of REW 5.1 Beta 13 is available for download from here.

Tip: Go to Help and make sure "Check for Updates on Startup" is checked so you don't loose on having the latest version. smile.gif

Along with bug fixes, there's some very interesting (to me) additions:

Beta release now supports OS X (tested on 10.5.8)
Order of measurements can be changed by clicking on the currently selected measurement in the measurement list and dragging it up or down to a new position
Added provisional support for Omnimic (untested) and added .omm as an accepted extension when looking for mic cal files
Added automatic detection of MiniDSP mic on OS X
Disabled manual SPL calibration when using calibrated USB microphones


Gentlemen, start your OmniMics?.......
post #504 of 9620
REW Fun Pic of the Day:



This is just a waterfall generated from my lousy experiments with the Audyssey mic hooked up to REW. Not a serious measurement, althought it has a kinda funny side. Please take a look at that little boo-boo at 50 Hz, the one that doesn't want to decay over time, but remains there constantly. You guess, it's a mains hum probably due to some slight ground loop in my system. Believe me it is inaudible at the MLP, ...but graphs never lie, eh? smile.gif

When we see this we will also be able to indentify without a doubt that the poster is either from Europe (50 Hz) or from NA (60 Hz). smile.gif

Funny isn't it? smile.gif
Edited by mogorf - 1/21/13 at 3:44pm
post #505 of 9620
Quote:
Originally Posted by sdrucker View Post


Along with bug fixes, there's some very interesting (to me) additions:

Beta release now supports OS X (tested on 10.5.8)
Order of measurements can be changed by clicking on the currently selected measurement in the measurement list and dragging it up or down to a new position
Added provisional support for Omnimic (untested) and added .omm as an accepted extension when looking for mic cal files
Added automatic detection of MiniDSP mic on OS X
Disabled manual SPL calibration when using calibrated USB microphones


Gentlemen, start your OmniMics?.......

 

Interesting.  If the OmniMic is now a viable option, maybe you guys can save some money!  Of course, the UMM-6 still has the custom calibrations...

 

So who is going to test this out?

post #506 of 9620
Quote:
Originally Posted by mogorf View Post

REW Fun Pic of the Day:



This is just a waterfall generated from my lousy experiments with the Audyssey mic hooked up to REW. Not a serious measurement, althought it has a kinda funny side. Please take a look at that little boo-boo at 50 Hz, the one that doesn't want to decay over time, but remains there constantly. You guess, it's a mains hum probably due to some slight ground loop in my system. Believe me it is inaudible at the MLP, ...but graphs never lie, eh? smile.gif

When we see this we will also be able to indentify without a doubt that the poster is either from Europe (50 Hz) or from NA (60 Hz). smile.gif

Funny isn't it? smile.gif

 

What is going on with those dips at 35 and 100Hz?

post #507 of 9620
Quote:
Originally Posted by LastButNotLeast View Post

Probably, but it's old news anyway, so I'm just going to start over like everyone else.

Unfortunately, the room is an acoustic nightmare: 15 x 30, open on one side to the kitchen, fireplace on the other side, cathedral ceiling and two skylights.

 

Solved my problem short-term: raised the noise floor to 65dB.

biggrin.gif

Michael

post #508 of 9620
Quote:
Originally Posted by mogorf View Post

This is just a waterfall generated from my lousy experiments with the Audyssey mic hooked up to REW. Not a serious measurement, althought it has a kinda funny side.

Hi Feri, here is one of mine first subwoofer waterfall graph yesterday.
post #509 of 9620

WARNING:  READ BEFORE CONDUCTING A 100DB MEASUREMENT!

 

Jason recommended a 60dB range on the vertical waterfall axis.  With a noise floor at 40dB, this means the REW sweep must be configured to run at 100dB.  To do this, I simply re-ran the REW mic calibration, adhusting the AVR master volume upwards until it registered 100dB on the SPL.  The final AVR MV level was +5! I then ran a 15-20,000Hz measurement sweep.  THIS WAS EXCEPTIONALLY LOUD.  Seriously, I was very concerned that I had damaged my speakers.  Jason, I think you should have provided some advance warning that measuring at such a level posed a risk of damaging equipment.  I would have been devastated if my expensive speakers had been harmed.

 

So, I backed the MV off to +0 (Reference), and ran a measurement at 95dB.  This was still very loud, but I was able to take measurements.  Here are the results:

 

Audyssey off:

 

 

Audysssey on:

 

 

Note that I have 60dB range on the vertical scale, and 15-300Hz on the horizontal scale, as per our agreement.  Note also that the time interval is maxed out at 1.5 seconds.  Either the waterfalls show that my room is a total piece of crap, or I am still missing something, because these graphs look significantly worse than the ones I posted earlier.

 

What confuses me is that the room and equipment haven't changed.  Just several different waterfall measurements and representations, and my room goes from good to bad.  confused.gif

post #510 of 9620
Quote:
Originally Posted by AustinJerry View Post

Interesting.  If the OmniMic is now a viable option, maybe you guys can save some money!  Of course, the UMM-6 still has the custom calibrations...

So who is going to test this out?

I have OM and it worked with my MacBook Pro and the latest release of REW...

I will also try it out with my windows based laptop with HDMI and compare it with my OM readings.

Thanks for your guide...smile.gif
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