[PD] vu-meter question

Roman Haefeli reduzierer at yahoo.de
Tue Aug 5 20:31:21 CEST 2008

On Tue, 2008-08-05 at 14:19 -0400, Martin Peach wrote:
> Frank Barknecht wrote:
> > 
> > For example as in the attachment.
> > 
> Interesting playing with that...If you give the osc~ a gain of 100dB, 
> which dbtorms translates to a gain of 1, then [env~] outputs 96.99dB and 
> the vu meter -3dB. To get 0dB on the meter you need to give 103dB to the 
> osc~, a gain of 1.413.
> My onboard soundcard starts clipping with the vu meter at -3dB, so a 
> gain of 1 on an osc~ is the maximum the hardware can handle.
> That is, maximum gain allowed by the hardware is 100dB ("sound pressure 
> level"), 1 ("full scale"), or -3dB (why not 0dB?).
> Why does env~ give an output that is 3dB less than, or 1/2 of, its input?

i think (correct me, if i am wrong) this is dependent on the crest
factor of the signal:


altough, the peak of the sine is 1, -1 respectively, the average (that
is what [env~] gives you) is lower,  3dB to be exactly. try the same
with a square wave and the result should pretty much be 0dB,
respectively 100dB.


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