Technical Decibel Question ???

Rorymonster

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:Wink3: Hello, hello, hello.

Was wondering if anybody could answer this question for me.

Scenario: You've been composing in Logic, Cubase or similar, and you decide that you want to spend some time mixing the tune, because you've added lots of tracks and it sounds a different to how it did. You've been pumping some tracks to get them heard over the others, and now's the time to turn everything down to a more suitable level, though the tracks are still at the right level in relation to each other. So you select multiple tracks in your mixer window and can lower the volume of all them by turning the highest one down by 3 dBs (for example). However, decibels are an exponential scale, and so 3 decibels between +3 and 0 is surely massively different to 3 decibels between -20 and -23.
So, does the sequencer or fader compensate for this? Or should one never try and change the levels of more than one track at once?

What is the best way to change the levels of more than one track at once? Can you link tracks together so that this is done for you? eg can you link a track to its bus so that the levels are always chnaged relatively together?

Cheers,

Rorymonster
 

Faction

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That's the point of the dB scale; a 3dB change has the same effect on percieved volume wherever in the scale it occurs. So taking the level down from 0dB to -3dB will change the volume by the same amount as taking it down from -20dB to -23dB.

However, it sounds like you're trying to solve a very simple problem in the most complicated way possible. If you're using Logic or Cubase (or anything with a 32bit internal signal path), and the general balance of the track is fine but everything is too loud, all you have to do is turn the master fader down until it stops clipping. THIS WILL NOT AFFECT THE QUALITY OF THE MIX IN ANY WAY.
 

Lazytom

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fink what my esteemed friend and colleague means is... if you want to turn down the levels of several tracks at once (all of which are at slightly different levels) but not the volume of the overall mix, will pulling down the fader on the top track cause the same relative decrease in volume in every track.

I think the answer is yes. But I'm not sure. Can't you tell when you pay it back? :P :Wink3:


the reason I think it'd be fine is partly that I'm sure those clever germans didn't overlook this issue...
 

Rorymonster

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Cheers guys, I got it. What I'm after is slightly different from what turning down the master will do, as individual tracks might be peaking even if the master is not.

But i got the answer I wanted: -3dB sounds the same anywhere on the dB scale, and that is why it is an exponential scale, so that this occurs. So if I turn down many channels at once, the amount that I change the loudest one will be the same as the amount that I change the quietest one.

Not the most exciting question ever I know!
 

Faction

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Even if individual tracks are peaking, they won't distort. You can have every individual channel on permanent peak, +20dB, and as long as the master channel is not peaking you won't (in theory) hear a single clipped sample. That's the beauty of a 32-bit audio engine.

Also, if you're using SX, bear in mind that adjusting linked faders in the way you're talking about is not accurate to the dB... you mix will change. Better just take the master fader down and hang the peak lights..
 

Rorymonster

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</div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Colin OOOD @ Feb 17 2004, 11:58 AM)</td></tr><tr><td id='QUOTE'> Also, if you're using SX, bear in mind that adjusting linked faders in the way you're talking about is not accurate to the dB... you mix will change. [/quote:bcdc3a9256]
Gotcha on your first point, but "not accurate to the dB" - what do yo mean? D'You mean that the dB value it displays is not accurate? :wacko: :Smile3:
 

Faction

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If you link faders and move them together, they will not all change by the same amount.
 

phlee

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</div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Colin OOOD @ Feb 11 2004, 06:15 PM)</td></tr><tr><td id='QUOTE'> That's the point of the dB scale; a 3dB change has the same effect on percieved volume wherever in the scale it occurs. So taking the level down from 0dB to -3dB will change the volume by the same amount as taking it down from -20dB to -23dB.

[/quote:331839954e]
That's because the ear has an approximately logarithmic response to amplitude, just in case anyone wanted to know that. Some think that accounts for it's huge dynamic range. Oh, and it's a logarithmic scale rather than an exponential one - the two are inverse to each other. Sorry, being pedantic again :rolleyes: :hehe:
 

TheBarrelShifter

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It's also important to remember that decibels are a relative scale, not absolute.

The term is often misused - You can only say that one sound is at +- x decibels compared to another, or commonly compared to a standard reference.

The actual definition of a decibel is 10 times the logarithm of the ratio of powers:
10 log (p1/p2) where p1 and p2 are the powers being compared.

When you talk of attenuating a signal by 3dB (or adjusting it by -3dB) you are using the starting volume as the reference, and the -3 as the ratio...

10 log (p1/p2) = 3dB
log(p1/p2) = 0.3
(p1/p2) = 10 ^ 0.3
p1/p2 = 1.99

In real terms this means that if you used a full scale digital since wave as the input, the peaks and troughs would be at +32768 and -32768 respectively - Attenuating the signal by 3dB would result in the peaks and troughs being at +16466 and -16466 respectively.
 

Rorymonster

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Cheers for the Barrelshifter - can't say that'll change my use of Logic though!!
Interesting... scratch scratch... sniff sniff...
 

soliptic

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</div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (TheBarrelShifter @ Feb 17 2004, 04:09 PM)</td></tr><tr><td id='QUOTE'> It's also important to remember that decibels are a relative scale, not absolute.
[/quote:e10cccef44]

*waves*

hello there!

yet another person i know already who turns out to be on here! this place amazes me!

:offtopic:


nice info about the dB scale btw... sort of thing i vaguely half understand but never really bother to learn properly :lol:
 
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