75dB channel levels. Why?

[UFObuster]

OK, I've leveled my 5 channels to 75dB (measured SPL) using the built in test tone. Everything sounds good and this appears to fall inside a comfortable range for my receiver's (Yamahs RX-V2600) master volume control. In auto set-up, the system actually produced a channel output around 80 to 85 dB. So, I've lowered it a bit. In practice, I find that I'm listening to a slightly higher master volume level now than before but the sound is fine.
..So, should I have set up to 85 dB? What exactly are the pros/cons for using 75dB? Are there some advantages or trade-offs re: amplifier out-put, dynamic range, etc that I need to know? Why is 75 usually considered for set-ups?
Thanks for input.

 

[MDS]

Dolby Reference Level is 105 dB PEAKS at the listening position and that is the level to calibrate to if you want true 'reference level'.

The test tone used for calibration in a receiver has an average level of -30 dB which means it is 30 dB below full scale digital (0dB). Not coincidentallly, the average level of the soundtrack of a movie on DVD is -31 dB.

Playing that tone and calibrating so that the channel levels read 75 dB on the SPL meter gives you reference level (75+30=105). The average level will be 75 dB and the peaks will be 105 dB.

 

[Dolby CP-200]

UFObuster

Yeah go for 85dbc and the keep the fader level at 0db reference level play Fight Club chapter 9 and watch the loudspeakers go into total distraction!!!!

Unless you know what to look for and listen for and that you have loudspeakers that can handle motion picture soundtracks to the loudest defying of all Armageddon levels. I would strongly say please don’t unless you can have the sound system set up with audio limiters that would prevent damage!

 

[MDS]

Ignore Dolby's post. For a 'former cinema projectionist' he doesn't know what he is talking about.

You would only calibrate to 85 dB if the test tone you were using is at -20 dB (AVIA calibration disc).

 

[Dolby CP-200]

How rude!

No I think he’s got the general idea.

 

[Savant]

Rude, indeed.

But you're both correct. Dolby CP-200 specifically refers to the C-weighting scale, in which case the "reference" level in question would be 85 dB. While no specific reference is made by MDS, the A-weighting scale is implied by stating a 75 dB "reference" level.

 

[MDS]

Rude because Dolby aka THX3417 never answers the question at hand but instead tells the newbies how they can't get true surround without something like his frankenstein setup.

Calibrating to reference level doesn't imply anything about A vs C weighting. You use C weighting when calibrating but the choice of 75 dB vs 85 dB depends solely on the average level of the test tone.

 

[Dolby CP-200]

like his frankenstein setup.

At least it works and would out do you. Any way calm down your not acting very professional.

 

[Dolby CP-200]

Oh come on MDS I’m only kidding come on, come back in.

There is one important factor that has been overlooked and no matter if UFO does sets all levels to a matched level of 70dbc or 75dbc is neither here or there.

The tone that’s what matters with matching loudspeakers for there three-screen it should sound like left channel ((HISS)) centre channel ((HISS)) right channel ((HISS)).

With mismatching left channel ((HISS)) centre channel ((hiss)) right channel HISS)).

Now I know that example may look crazy, try doing it with your mouth three times via changing the pitch via slightly adjusting the lips the tone will change.

Also placing your hand in front of you mouth while hissing and moving it away (doppler shift).

This is the same deal with the loudspeakers but it can be solved.

So UFO may get it to register at 75dbc for each of the fronts and the fronts are very important, this is where sound mixers bust there butts over hundreds of hours to produce the finest Dolby mix one could possible hear.

 

[Guiria]

So is it necessary to adjust the channel level trims so that 75 db plays at the 0 db mark on the receiver? I just have a mental note that 75 db is -14 on my receiver for 'reference level'. If I'm missing something please advise!!!

 

[MDS]

You can use whatever number on the volume scale you want but 0 is the convention. If you calibrate so that 0 on the volume scale is reference level then you know just by looking at the display that -14 is 14 dB below reference.

THX receivers and many higher end models always play the test tone at what would be 0 dB on the volume scale so in those cases you have no choice but to use zero unless you use a calibration disc instead of the internal test tones.

 

[Dolby CP-200]

Guiria

It’s good that some have the db indicator to display it in db. Question what AVR are you running I’m running the Kenwood KRF-X9050D THX select.

 

[Guiria]

You can use whatever number on the volume scale you want but 0 is the convention. If you calibrate so that 0 on the volume scale is reference level then you know just by looking at the display that -14 is 14 dB below reference.

Man you guys are quick.

MDS, this explains it right on the money.

As for Dolby CP-200's question; I'm running the Yammy HTR-5960. Volume is displayed in db...aren't most AVR's?

 

[Dolby CP-200]

You can use whatever number on the volume scale you want but 0 is the convention. If you calibrate so that 0 on the volume scale is reference level then you know just by looking at the display that -14 is 14 dB below reference.

THX receivers and many higher end models always play the test tone at what would be 0 dB on the volume scale so in those cases you have no choice but to use zero unless you use a calibration disc instead of the internal test tones.

That’s true unless you what splitting headache within a few minutes, which is why I use outboard amplifiers with audio limiters and EQ and the odd active x over for the time being.

The amplifier levels are set to still equal the level but the gaol of the audio limiter is to protect the three-screen from being damaged and it may limiter the soundtrack but I have gotten past that issue and deepening on the type of Dolby film mix, films like “Armageddon” where the dialogue is recorded on the high level may sound too harsh on most home cinema set-ups.

I often play the film at -6db on the fader it’s the over loud dialogue in the film, which is probably why it lost best sound in 1998 maybe.

So there are many factors to consider rather than keeping to a topic, this is the whole topic setting the levels on the fader on the AVR and remembering that level.

All Dolby CP units are set to fader “7” which is the standard 85dbc level for all cinemas. I myself had to always set some films at fader 5.5 because the chief projectionist thought that “Tango & Cash” was too high a level for a Dolby SR. Well let’s but it this way it sounded too bright in the cinema like most of the 10 screens.

 

[Dolby CP-200]

Guiria

If you what the mother of all splitting headaches play Die Another Day at -14db on the Yamaha I’ll bet you £1.00 you’ll be forced to turn level down below -20db! Its bloody too loud knife throwing towards the end of the film, where Miranda Frost is lobbing knifes towards Jinx at 8KHz and the dynamic range during that sequence is just crazy knifes do not make that harsh sound!

 

[Kolia]

And I though the 75dB thing was just to balance the sound volume ?!?

Even if I can adjust the front left and right levels, I just set the receiver’s level to whatever will get 75dB out of the fronts, and adjust the center, surround and sub to match…

Am I missing something? Who cares if -14dB on the receiver’s display is actually 75dB from each channels?

 

[MDS]

Am I missing something? Who cares if -14dB on the receiver’s display is actually 75dB from each channels?

You would only care if you want to know what number on the volume display is 'reference level'. If you used the internal test tones and 75 dB SPL reading you have Dolby Reference Level, but you can use whatever SPL you want as your 'reference'. The relative volume display (negative numbers) is just a convenient way to tell where you are relative to the reference.

If all you want to do is balance the channels then it doesn't matter what volume setting you use or what SPL reading the meter shows - just make them all equal. If you do calibrate to reference level, that doesn't mean you have to actually listen to it that loud - I never do.

 

[Savant]

MDS:

Calibrating to reference level doesn't imply anything about A vs C weighting. You use C weighting when calibrating but the choice of 75 dB vs 85 dB depends solely on the average level of the test tone.

What standard dictates that all receivers use a -30 dBFS calibration signal? Presuming there is such a standard, is it safe to assume all receivers are adhering to it? The only reason I ask is because the Dolby literature I've been going through appears to imply a "standard" of -20 dBFS for pink noise calibration. But I am not familiar with what standards, if any, would govern this sort of thing. Any thoughts?

You also mentioned earlier in the thread that:

...the average level of the soundtrack of a movie on DVD is -31 dB...

There would appear to be ample research that suggests this isn't the case for all DVDs. So is this a standard by which DVDs should be produced, or is it actually the case for all DVDs?

Please note that I'm not trying to be a d1ck or anything. Just trying to understand this better myself!

************

Koila:

Am I missing something? Who cares if -14dB on the receiver’s display is actually 75dB from each channels?

Others may feel different, but, IMO, it is always best to have the signal level well above the noise floor and, at the same time, have it set such that program material will not send your amp(s) into clip. If you set the reference too low, you run the risk of getting too close to the noise floor of the equipment. Granted, this is an unrealistic scenario for most equipment these days since the amount of gain trim on a given channel is usually limited to 10-30 dB (looks like about 12-20 dB on your Yamaha).

The other problem, that of clipping, is very real. If you decide, for example, to set the highest possible master volume level (+16.5 dB on your Yamaha receiver) as the "reference," then peak levels in the program could clip your amplifiers. Not pretty.

Bottom line is there are sound reasons for using 0 dB on the master volume as the reference level. Listening at 85 dBC (or 75 dBC for that matter) is probably not going to be comfortable. Thus, if you set "reference" to -14 dB on the master volume, you may find that your comfortable listening level is somewhere south of that. Whereas setting "reference" to 0 dB on the master volume allows you to get more S/N, but still not run the risk of clipping. Again, this may not matter much in the grand scheme of things - equipment S/N ratios are comfortably high these days (<80 dB on your Yamaha). I have, in the past, set "reference" to -15 dB or thereabouts on different receivers and had no problems with the system.

Make sense?

 

[Jack Hammer]

I'm a little confused about the whole setting reference level thing. I'm using a Denon 2805 reciever. When I calibrate it, I usually start first with the external mic and internal test tones then I follow up and fine tune with the Avia's discs tones using my Radio Shack analog meter. Am I supposed to set the volume to "0" before I start? I've never touched the volume for the internal tones (I've done it anywhere from -35 to -10, no difference that I could tell in how the avr calibrates). For Avia I think it's around -10 or -12, I forget.

I rarely listen at a volume above -18 (loud for my place), occasionally ~-14, but that is extremely rare. Then again, I am in a tiny place. I should probably know this, maybe I do am I am having a brain fart, but how would I calibrate it to "0"?

Jack

 

[MDS]

What standard dictates that all receivers use a -30 dBFS calibration signal? Presuming there is such a standard, is it safe to assume all receivers are adhering to it? The only reason I ask is because the Dolby literature I've been going through appears to imply a "standard" of -20 dBFS for pink noise calibration. But I am not familiar with what standards, if any, would govern this sort of thing. Any thoughts?

The -30 dBFS test tone signal is actually a THX standard but most receivers (even non-THX) follow that standard.

Yes, -20 dBFS is the Dolby standard and with that you would then calibrate so that the SPL meter reads 85 dB. AVIA is the only disc that I know of that uses -20 dBFS. DVE and internal test tones are -30 dBFS. IMO the narrative on AVIA confuses people because they say calibrate to 75 dB because 'reference level is too loud for most people'. If you do that, you will get 95 dB peaks which is not quite Dolby Reference Level.

There would appear to be ample research that suggests this isn't the case for all DVDs. So is this a standard by which DVDs should be produced, or is it actually the case for all DVDs?

DVD mastering that doesn't follow the standard? Nah, say it isn't so.
Yes, I think that -31 dB is supposed to be the long term A weighted average level of dialog but isn't universally followed. The bitstream is also supposed to have a DialNorm value that accurately reflects the difference between the actual dialog level and -31 dB but I'm sure that is not universally followed either.

I agree completely with the rest of the comments about using 0 dB as the reference volume setting. 0 dB on the volume scale is nowhere near the max output capability of the receiver. If you are going to use the relative volume display its benefits are lost if you use anything other than zero. If you were to use -14 as the 'reference' then when you are listening at -24 you have to do the math in your head: my reference is -14 but the level is -24 so 24-14 = 10; I am 10 dB below reference. Same problem with using the absolute volume display - my receiver only uses absolute and the reference level is 60 so when I set it to 40, I have to calculate that I am 20 dB below reference.

Not that any of this really matters...you set the volume you want and forget it but sometimes you might be curious where you are relative to reference level and the relative display makes it easy to see at a glance (if you used 0 as the reference volume level).