Audio Calibration

[Velcro]

I resently calibrated my audio output with a borrowed Radio Shack SPL meter 33-4050 and both the Digial Video Essentials DVD and Avia DVD. I noticed that when all the spekers are set to the same volume for one disk they're not the same for the other. Why is this?

My guess would be that they use different pitches in thier test signal and that the accustics of the room are not flat. Given this I would think that the Receivers equalizer (many bands but I don't rememberthe number) should be used to balance this out. I have not found any info on doing it for 5.1 however I seen comments on this site not to do. So whats the scoop? If it should be equalized, whats the method for doing this? The DVD's don't go into this. They also don't seem to have the proper test tones for eq setup. Any recommendations?

thanks
MikeB

 

[MACCA350]

The Reference Test tones for Digital Video Essentials DVD and Avia DVD are mastered at different levels. One is meant to be calibrated at 85db the other at 75db(cant remember which is which, and cant be bothered checking my avia disc)

cheers

 

[MDS]

MACCA350 is correct. AVIA test tones are at -20 dB and DVE are at -30 dB. The internal test tones of the receiver are at -30 dB (so I try to remember which is which between avia and dve with the mnemonic 'DVE Internal'; ie DVE test tones are at the same level as the internal test tones).

 

[Velcro]

Since the DVDs are mastered for different DB levels I would think that switching from one to the other would result in a different level in the SPL but I would still expect all speakers to read the same level for each disk.

The problem I'm seeing is not a master level difference but an individual speaker difference. So for example, on one DVD all speakers are set to have the same DB level. Then switching to the other DVD if I assume the center channel level is now +0 then the Left main is +1 DB, the right main -1, the right rear -2 the left rear -1 different from the center channel. Each speaker changed independantly of the others. I would have expected all the speakers to keep the same level relative to each other.

Why should the speaker levels drift independantly when switching DVD?
thanks

 

[MDS]

Since the DVDs are mastered for different DB levels I would think that switching from one to the other would result in a different level in the SPL but I would still expect all speakers to read the same level for each disk.

Why should the speaker levels drift independantly when switching DVD?
thanks

I'm not sure I follow you here.

If you use AVIA and calibrate so that the SPL meter reads 85 dB, then switch to DVE, the meter would read 75 dB (because the level of the test tone is 10 dB lower).

Once you set the channel levels, they should not change for ANY disc. The SPL reading on the meter will of course vary with the level of the disc you are playing, but if after calibration you have mains=0, center=+1, rears=+2 (just as an example), then they should remain that way.

The only way they would change is if you were to then run auto calibration (if your receiver has it) or you press the channel level up or down buttons on the fly as you are listening. With most receivers, on the fly adjustments are cancelled when you put the receiver in standby.

 

[Velcro]

I didn't do a great job of explaining but I think this will clear it up.

If I use AVIA and calibrate so that the SPL meter reads 85 dB.
Then I switch to DVE.
I would expect each speaker to read 75 dB (because the level of the test tone is 10 dB lower).

What I find is that the center reads 75 db, but the right main is 73 db, the left main is 76 db, the left rear is 77 db and the left rear is 74 db.

If I go back to AVIA all speakers read 85 db.
My system has no automatic calibration. So the only thing I can figure is that the tones the two DVDs produce have different frequence content and therefore the speakers and room react differently. Or is there some other reason?

 

[MDS]

The test tones for both AVIA and DVE are pink noise so the frequency content should be identical. Pink noise has equal amplitude at every octave.

I would say you don't have a problem at all. It is next to impossible to get every channel to read exactly 75/85/or whatever you choose dB. If you can get them to within 1 dB of your target that is extremely good.

You also have to remember that the tone plays for only a second or two before it moves to the next channel. In the instant before the switch, the SPL will drop until the tone for the next channel ramps up. You may have to go through all the channels multiple times, trying to get a fairly steady state reading around your target.

If you let the tones cycle for awhile when using AVIA, I think you will find that the values fluctuate slightly too.

 

[mtrycrafts]

I didn't do a great job of explaining but I think this will clear it up.

If I use AVIA and calibrate so that the SPL meter reads 85 dB.
Then I switch to DVE.
I would expect each speaker to read 75 dB (because the level of the test tone is 10 dB lower).

What I find is that the center reads 75 db, but the right main is 73 db, the left main is 76 db, the left rear is 77 db and the left rear is 74 db.

If I go back to AVIA all speakers read 85 db.
My system has no automatic calibration. So the only thing I can figure is that the tones the two DVDs produce have different frequency content and therefore the speakers and room react differently. Or is there some other reason?

What happens if you calibrate with DVE, then check to see what Avia produces? Are they still off from each other about the same amount?

It would appear that one of the test disc is not well mastered. 2 dB is a pretty big difference.

 

[Velcro]

These numbers where just for example. I unfortuantly don't remember the actual numbers. I'll see if I can reborrow the disks and post the real numbers.