75dB channel levels. Why?

[MDS]

Jack Hammer

If changing the master volume setting has no affect on the loudness of the internal test tones then your receiver is one that automatically sets the volume level at 0 dB. So when using the auto-setup or doing it manually via the internal test tones, you are calibrating so that 0 on the volume display is reference level.

If you want to set it at any number other than 0 you'd have to use an external calibration disc like AVIA or DVE.

Say you think that the tones are just too loud and annoying but you do want to use 0 as the reference volume setting. Just use the calibration disc so you can control the volume and set the master volume at -10. Then calibrate so that the reading is 10 dB lower than what the target would normally be. If using AVIA, the test tones are at -20 dBFS so you'd normally want the SPL meter to read 85 dB. If you set the volume at -10 but get a reading of 75 dB on the meter that is the same as 85 dB at 0.

 

[Jack Hammer]

...
Say you think that the tones are just too loud and annoying but you do want to use 0 as the reference volume setting. Just use the calibration disc so you can control the volume and set the master volume at -10. Then calibrate so that the reading is 10 dB lower than what the target would normally be. If using AVIA, the test tones are at -20 dBFS so you'd normally want the SPL meter to read 85 dB. If you set the volume at -10 but get a reading of 75 dB on the meter that is the same as 85 dB at 0.

Thanks for the clarification, that's pretty much what I thought, but I wasn't sure. I don't recall what # I use when I calibrate (70,75,80,85db), because I haven't done it in a while. But I plan on doing it again in the near future to compensate for some new panels I just added and a second sub. Plus I'm thinking of channging my mains.

Wow, it just occured to me that I usually listen ~-20db. That would mean I am 20db below reference. I can't wait to get a bigger apartment (325sf/2200cf incl bedroom, hall, and bath!).

Jack

Jack

 

[Savant]

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.

Which would assume that the absolute volume increments are actually decibels... I find that is not always the case, unfortunately.

Anyway, thank you for your insight.

***

Going back to the weighting discussion briefly, I wanted to clarify that all this discussion of "reference" level does, then, assume the use of the C-weighting scale on the sound level meter. Using A-weighting would require some adjustment. I only mention this because I believe the Goldline reference DVD (the "Audio Toolkit") - if anyone's using it - recommends the use of the A-scale for level setup and adjustment. I am going from memory here - I haven't used the Goldline disk on quite some time. Regardless, I believe their justification for using 75 dBA as the "reference" was that the SPL measured on the C-scale will generally be 10 dB lower than the equivalent SPL measured using the A-scale. That was the main reason I referred to it earlier. Sorry to have caused any confusion.

 

[j_garcia]

I'm not sure why there is even a discussion on this. MDS has pretty much nailed this one down nice and neat.

 

[Savant]

I'm not sure why there is even a discussion on this. MDS has pretty much nailed this one down nice and neat.

Agreed, as it pertains to the original question.

However, I, for one, like to understand something as completely as possible - and help others to do so where possible. Hence my annoying persistence. If it's more appropriate to continue the discussion offline, I would not be opposed.

 

[j_garcia]

No, I don't think it should be taken offline, because the information here is certainly useful.

The Avia disc threw me originally as well. My receiver is THX, so I just use the internal tones.

 

[Dolby CP-200]

Set the level to 75dbc and add on the films soundtrack, what is that going to equal? Depending on the sensitivity of the three-screen its going to be very toppy in most cases I’ll assure you.

 

[MDS]

Set the level to 75dbc and add on the films soundtrack, what is that going to equal? Depending on the sensitivity of the three-screen its going to be very toppy in most cases I’ll assure you.

It's going to equal 75 dB when the average level of the soundtrack is equal to the average level of the test tone that was used to calibrate. It's going to equal 105 dB when the level of the soundtrack hits a peak (0 dB). That is what calibration is all about.

The level of the soundtrack will of course vary from very low levels all the way up to 0 dB but by definition it cannot go higher than 0 dB.

 

[Dolby CP-200]

Not from what I have seen with films from the late 1990’s Armageddon

that film was getting a lot heat during 1998 and a few others films as well.

 

[MDS]

Since you mentioned speaker sensitivity, let's go with that idea. The whole idea of calibrating is to setup the system so that if you choose to listen at reference level you will get 105 dB peaks at the listening position. Obviously, calibration takes into account the sensitivity of your speakers and room acoustics - after all you are playing the test tones.

Let's say for the sake of illustration that after calibration your front channel trims ended up at +3 and your speakers had a sensitivity of 90 dB. If you replace those speakers with new speakers that are 93 dB sensitive, of course the peak level will change; anytime you change speakers or alter your room in any way you must recalibrate. If the speakers were the only thing that changed, then your new channel trim setting will now be zero because the speakers are 3 dB more sensitive and thus require less power to reach the same SPL.

What I suspect you are really getting at however, is the average level not the peak level. The peak level can never exceed your calibration level because 0 dB is the highest that the digital audio signal can reach.

If you calibrated using a -30 dBFS tone so that the SPL meter reads 75 dB then 75 dB is the *average* level and it will only be 75 dB when the soundtrack level is also at -30 dB. Now the particular movie to which you referred may have an average level greater than -30 dB so it will be louder on average but it cannot ever exceed the peak level.

Want to verify what I am talking about? Do the proper calibration and then play a music CD. The average level of modern CDs is typically around -12 dB which is WAY louder than the average level of the test tone that was used for calibration. Watching a normal movie, the average SPL will be about 75 dB (that's what you calibrated to after all). When playing a music CD, the average SPL will be closer to 95 dB (because the CD is almost 20 dB hotter to begin with).

 

[Kolia]

Koila:

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?

I’m not the one with a Yamaha receiver.

So basically, setting the reference to 0 dB is just to standardize the listening volume display. Maybe my receiver’s different? Volume goes from -69dB to +18dB. I get my 75dB at below zero (about -14dB) which puts it outside of the +/- 12dB channel adjustment range. I can’t zero it.

If it’s clipping I’m afraid of, I’ll just limit my volume my self. Or at least base my volume setting on the loudest speaker so that one doesn’t go to high. Then again, what good will this do? If a given system can’t peak as high as the owner’s like’s to play his movies to, it’ll clip anyways. I don’t see what kind of protection that would afford.

 

[Savant]

If it’s clipping I’m afraid of, I’ll just limit my volume my self. Or at least base my volume setting on the loudest speaker so that one doesn’t go to high. Then again, what good will this do? If a given system can’t peak as high as the owner’s like’s to play his movies to, it’ll clip anyways. I don’t see what kind of protection that would afford.

Looked up the specs on your components. Let's look at this clipping issue for a moment...

Say you "calibrate" your system to a reference level of 75 dB at your listening position, which is, say, an average of 4 m from any given loudspeaker. This (approximately) equates to a level of 87 dB at 1 m. Based on your loudspeaker sensitivity, this works out to be about 0.4 W of power to drive the speakers at steady-state reference of 75 dB. Assuming +30 dB peaks, the loudspeakers set at reference level will need 20x (3 dB = 2x) the power to handle those peaks, or 8 W. IMO, 8 W is unlikely to drive your amps into clipping. The dynamic headroom available from your receiver appears to be on the order of 120 W or so. (NAD didn't offer a rating for your loudspeakers' 6 Ω load.) So, you've got about 112 W - or an additional 21 dB or so.

Now, to the topic at hand, if you set 0 dB as "reference" and you're able to "crank it up" another 18 dB above that, you should have some room to spare with regards to clipping. Your ears might be bleeding at that point, but your receiver will not fry!

Alternatively, if you set -14 dB as "reference" and have, now, an additional 32 dB of "crank it up" available, then you could run the risk of clipping if you turn the master volume up above about +7 or so.

For others following along with their TI-83s in hand, these are back-of-the-envelope calculations, so please don't be too cruel!

 

[Kolia]

Looked up the specs on your components. Let's look at this clipping issue for a moment...

Say you "calibrate" your system to a reference level of 75 dB at your listening position, which is, say, an average of 4 m from any given loudspeaker. This (approximately) equates to a level of 87 dB at 1 m. Based on your loudspeaker sensitivity, this works out to be about 0.4 W of power to drive the speakers at steady-state reference of 75 dB. Assuming +30 dB peaks, the loudspeakers set at reference level will need 20x (3 dB = 2x) the power to handle those peaks, or 8 W. IMO, 8 W is unlikely to drive your amps into clipping. The dynamic headroom available from your receiver appears to be on the order of 120 W or so. (NAD didn't offer a rating for your loudspeakers' 6 Ω load.) So, you've got about 112 W - or an additional 21 dB or so.

Now, to the topic at hand, if you set 0 dB as "reference" and you're able to "crank it up" another 18 dB above that, you should have some room to spare with regards to clipping. Your ears might be bleeding at that point, but your receiver will not fry!

Alternatively, if you set -14 dB as "reference" and have, now, an additional 32 dB of "crank it up" available, then you could run the risk of clipping if you turn the master volume up above about +7 or so.

For others following along with their TI-83s in hand, these are back-of-the-envelope calculations, so please don't be too cruel!

Wow, you put a lot of work in that reply!

Thanks, it's all clear in my little head now...

 

[SNAKE]

This has been an interesting thread to read,i havent used the auto setup on my Denon ,should I ? i have just been adjusting levels that sounds good to the ear.Will i notice a seat of the pants difference in sound if i set it up with the micraphone?

 

[mtrycrafts]

This has been an interesting thread to read,i havent used the auto setup on my Denon ,should I ? i have just been adjusting levels that sounds good to the ear.Will i notice a seat of the pants difference in sound if i set it up with the micraphone?

Either the auto setup or a manual setup with a spl meter, yes, you should.
By ear, you can be off a lot.

 

[SNAKE]

Either the auto setup or a manual setup with a spl meter, yes, you should.
By ear, you can be off a lot.

Ok,iam curious now,after i do auto set-up does it default to that setting or do i have to save it as a favorite?I dont know if it tells that in the O/M er not.