[PD] from signal to VU

Thomas Grill t.grill at gmx.net
Wed Feb 12 17:43:04 CET 2003


> On Wed, 12 Feb 2003, Alex from Idoia wrote:
> > I am trying to use VU to measure the output of a signal.
> > Is there an external like Max for [log~] or even [gain~]. ?
> > I am trying to do the conversion db=log10(signal between 0 and 1)*20.
> > Is there another way ?
> > Thanks
>
> Hi, I've been wondering about this: how does square root and logarithm
> work for signals, because signals may get positive or negative... which
> means taking square roots of negatives (imaginary result), taking logs of
> numbers very close to zero (big negative result), equal to zero (minus
> infinity result), smaller than zero (complex result)... I mean, the signal
> itself is not complex, so how does applying square root and then applying
> square get back to the original signal? (maybe the answer is: it
> doesn't...)

Don't know if it's what you wanted to know, but in typical musical or
acoustic applications one would not take the instantanous sampled signal but
an envelope or average of the absolute samples over some (small) timespan
("RMS value"). Thus, sqrts or logs of negative numbers can't occur. The only
case is rms=0, which is easily treated as a special case (e.g. -1000 dB)

T





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