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how do you know what "reference" sound level is?

1714 Views 22 Replies 15 Participants Last post by  hometheaterguy
my friend mentioned it when i was at his house the other night. then i read something about it on the forum. is there come decibel level at the seating area that is considered "reference"?
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With the system calibrated to 75dB on the test tone (00dB on the display during calibration) then master set to 00dB whilst watching a film. Although usually that's far too loud, -20 to -15dB is about right, (for me) as some are recorded hot, and some not (ie Toy Story 2) where -15 for my normal level.
Originally posted by Sc0rp10n
my friend mentioned it when i was at his house the other night. then i read something about it on the forum. is there come decibel level at the seating area that is considered "reference"?
Reference level is defined as 85db with peeks going to 105db. You calibrate your system to produce this sound level when your volumn control is at 00

Try watching the Star Wars Pod Race at reference level with a high end subwoofer like a SVS PB2 ... Its a different movie.. :)

Hope this helps..
All replies are great, Dolby defines their own reference level as volume level of an audio system with the volume at the 0 decibel setting resulting in 85 decibel volume with a test tone and 105 decibel peaks. Dolby reference level is the volume level used in movie theaters for movie presentations (although this level is sometimes turned down).

The reference level is set using a test tone generated by a surround sound preamplifier and a sound pressure level meter (SPL meter) to measure the sound output or volume. While providing a realistic and enlivening auditory experience, the reference level is very loud and is often turned down somewhat by listeners. However, surround sound audio systems should be set to the Dolby reference level and all channels properly equalized (each channel putting out the same sound pressure levels with a reference signal) even if the system will not be listened to at the true reference level
00dB on the display is not a prerequesite for being at reference level.

in fact, that displayed reading is sorta meaningless, except for relative purposes. among many other things, the distance from the speakers to the listening spot, the room size, and the amount of power you have affect and dictate what volume level setting is necessary on the receiver/pre/pro to achieve "reference level" volume at the listening spot.

most people calibrate their system such that the left front speaker's individual level setting on the receiver/pre/pro is left at 0.0dB. the volume on the receiver is raised until the test tone from that speaker reaches reference level, WHATEVER that volume setting may be.

are you guys suggesting people force their receiver/pre/pro to display a 00dB setting when at reference level by raising or lowering the levels of all the individual speakers by whatever it takes to achieve that? certainly not? i would expect this to be impossible, even, in some cases.

it sure would be nice if the manufacturers would allow us to recalibrate the display to read 00dB at each of our own individual reference levels, though.
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i'm totally confused now. i have a denon 3805 that i have yet to turn on. still waiting on my rear/side surrounds and my television all to be delivered next week. are you saying that i'll have to play a "test tone", measure it on a SPL meter, and when the meter reaches 85db hit some kind of "reset" button on the receiver that makes the volume level read 00?
Originally posted by Sc0rp10n
............ and when the meter reaches 85db hit some kind of "reset" button on the receiver that makes the volume level read 00?
no! sorry to confuse. i said it would be nice if that was an available feature.

the first part of your statement is correct, though. you increase the volume on the receiver until the spl meter reads 85dB (or 75dB) at your sweet spot. whatever that setting is, THAT is your reference level volume setting. if you want to view a movie at reference level, that's where you set the volume.
so is it possible to get the receiver display 00 when it is playing at reference level (i.e. loud)? i have the denon 3805.
My receiver actually does this automatically (though it is not an auto calibrating unit). If I engage the test tones, the volume automatically rises to 0dB on the display. From there, the receiver manual suggests calibrating each channel to 75dB from the primary listening position. After calibration is complete, each channel reads 75dB from the primary listening position when I cycle through the tones (the sub tone actually reads a few dB less, so I adjust it accordingly).
It should be reiterated that 75 db on the SPL meter is perfectly acceptable for calibration, in case you find 85 db to be too loud. I personally find those test tones even at 75 db give me a headache after a round of calibration.

Originally posted by Sc0rp10n
so is it possible to get the receiver display 00 when it is playing at reference level (i.e. loud)? i have the denon 3805.
it depends. if this is in a closet-sized or stadium-sized room it may be difficult to adjust each individual speakers' level far enough to compensate. they only allow you so many dBs in either direction. you wouldn't want to do that, anyway.

most people don't harp on what actual setting their receiver is at when their reference speaker (the one whose individual level is left at 0.0dB; usually the left front) is at reference level. if it's 00dB, great. if it's off by a few dBs i suppose if it's so important to you, you can adjust it out by adjusting all the individual speaker levels by that amount. but most people don't worry about it.
I have a 3803 so I think it is similar to the 3805 (although I thought you can get a optional mike and the receiver will auto calibrate, but I might be thinking of speaker delay). Anyway there's a menu that displays the speaker setup and plays the test tones. This will automatically cause the receiver to 00. Then just adjust level of each speaker to 75dB or 85dB on the SPL meter.

When I adjust my speaker level with test tones to 75dB and then calibrate with Sound and Vision Theater Tune-up (Ovation) the calibration never matches. Anyone know why that is?

00 is very very loud!
For reference level how loud you calibrate the test tones to depend upon the level of the test tones themselves.

For a test tone that is -20dB the system would be calibrated to 85dB at the listening position. If the tone is -30dB then the system is calibrated to 75dB at the listening position.

For THX certified receivers/processors follow the instructions in the manual for calibration. After you do that 00dB on the main volume control is THX Reference Level. From there it will also tell you how many dB below reference you are. For example if you watch a movie at -10dB on the main volume control that means the loudest peaks will be 10dB below THX reference level... so instead of peaks at 105dB for the main channels your peaks would be at 95dB.

note, scorpion, that people with separates and the ability to adjust their individual amps' outputs may be able to achieve the 00dB reference level volume setting that you're asking about much more easily than those with receivers.

with a receiver, whatever it takes to get that tone to reference level is your reference level volume setting.

now, how the newer, self-calibrating receivers handle this, i'm not certain. they may, indeed, recalibrate the displayed volume at reference level to 00dB for you.
oh, i plan on letting it calibrate itself using the optional speaker. hopefully it'll do that.
There is some confusion here. If you're using the internal test tones generated by your THX pre-amp, you should set your sound levels for each speaker at the listening position to 75dB SPL. If you are generating the test tones externally, then use 85dbSPL. The internal test tones in a THX processor are set up to allow you to use 75dB during your set up; but, are actually setting an 85dB reference level. This compensation in the internal test tones was done to make it easier on your ears (and speakers).
Dennis. Great clarification.
This is great information.

I'm happy to read that others don't listen at reference level either. The closest I've been to 0db has been -4db. Of course, how close I can get to 0db depends on the source. As it was mentioned, some sources are hotter than others.
I'm happy to read that others don't listen at reference level either
At least not when anyone else is home...:)

The "0db" doesn't actually refer to the receiver readout at all. Sfogg has given the most accurate explanation so far.

Digital audio is stored such that "0db" is the loudest possible sound. All other recorded sounds are stored RELATIVE to the zero db mark. So, -20 db is 20db quieter than the audio format is capable of storing. Most test tones are recorded at either -20 or -30db, meaning that you should calibrate w/ your SPL meter at 85db or 75 db, respectively, to make it so that audio recorded at the 0db mark will play at 105db, and that the quieter sounds will scale down from there. 75db and 85db are NOT reference levels. They're just common levels to match at because they won't piss off your neighbors or kill your ears (mainly the latter, since mixing studios and movie theaters don't have to worry about neighbors, and they're the ones who are defining all these numbers for us to worry about).

The "0" on the receiver often is the manufacture's attempt to line up their readout with all these ideas, and they're often close (for me, -3 or -2 on the receiver is reference, because at that volume, a 0db recorded sound will play at 125db at the listening location... but my speakers are sensitive, so for some people that "0" on the dial may actually correspond perfectly). Either way, the number on the receiver is a nice gesture, but arbitrary.

In my opinion it is incorrect to balance your system based on these reference levels if you don't listen at them (which few people do). It's important to MIX at these high volumes because you don't want to let a bad sound go unnoticed that might end up being heard in a theater, but if you find yourself listening to music and movies with the dial around a certain spot, balance your speakers there, because that's where you want it to sound best. See what your front speakers play the test tones at, and match the other speakers to that. Don't feel inadequate because your SPL meter is reading much lower than 75db. Remember, those test tones are not recorded at full volume!

As for some sources being "hotter," this is true, although it's more of an analogue term, which is a whole other conversation. Not all digital recording will hit 0db. Some won't even come close. It really depends how it was mixed. Dialog can be normalized to a variety of different levels for movies, and if (God forbid) the movie finish without anything exploding, it may be really far from it. Songs can be compressed to push more of everything closer to the 0db mark, which make them sound louder while sacrificing dynamics, which is common practice in the pop world. In their favor, this does maximize S/N ratio as well.

Just some ideas to chew on.
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