[PD] vu-meter question

Roman Haefeli reduzierer at yahoo.de
Tue Aug 5 22:14:58 CEST 2008

On Tue, 2008-08-05 at 15:23 -0400, Martin Peach wrote:
> Roman Haefeli wrote:
> > 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:
> > 
> > http://en.wikipedia.org/wiki/Crest_factor
> > 
> > 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.
> Yes, that makes sense. That's why in analog equipment you try to stay 
> around -3dB instead of 0dB because the peaks are at 0dB. In analog you 
> can go above 0dB with progressively reduced gain, but in digital 
> equipment you get hard clipping at exactly 0dB, so it's nice to know 
> when it's happening. [env~] will give different output depending on the 
> waveform it's measuring, so it's not too useful for determining if 
> overload is occurring.
> Maybe [peak~] from flib is appropriate for that, but it seems to involve 
> doing an fft so it may be computationally heavy.
> I'm still not able to instantiate [>~] from zexy...

on extended? which version? from what i heard, extended-0.40-rc4 doesn't
suffer anymore from this problem. [>~] from the multiclass library
should work well, no matter what version.


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