[music-dsp] Decibel Question - Thanks!..... and another Question :-)

Sampo Syreeni decoy at iki.fi
Sat Apr 6 05:28:14 EST 2002


On Thu, 4 Apr 2002, James Chandler Jr. wrote:

>The ear hears levels in an approximately log fashion, so a log meter
>represents levels similar to the way the ear judges relative levels.

This is an issue with which I've burnt myself more than once, but I think
this relationship does not hold for all sound levels. You will need an
additional power function on top of your logarithm to get it right -- the
exponent is something like 0.6==3/5. (This is why faders in pro mixing
gear have nonlinear dB scales -- the scale is usually a piecewise linear
approximation to f(x)=x^(5/3).)

>One can often hear very quiet instruments mixed with much louder
>instruments. Ferinstance a finger cymbal track in a mix might be many dB
>quieter than the bass track.
>
>Using linear meters, if the bass track is displaying full-code on the
>meter, the finger cymbal track might be so quiet that you don't even see
>any meter activity.

We should also note that the threshold of hearing isn't constant -- you
will need a lot of bass power to get the same loudness as a cymbal with
lots of mid frequencies. At the very minimum, you will have to filter
("weight") to compensate. Higher end loudness measurements also do masking
calculations and the like. Nothing's ever simple...

Sampo Syreeni, aka decoy - mailto:decoy at iki.fi, tel:+358-50-5756111
student/math+cs/helsinki university, http://www.iki.fi/~decoy/front
openpgp: 050985C2/025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2


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