[PD] max value of last n samples
reduzent at gmail.com
Sat Feb 3 10:33:42 CET 2018
On Sam, 2018-02-03 at 02:47 +0000, Dario Sanfilippo wrote:
> Thanks, Roman.
> On 2 February 2018 at 21:28, Roman Haefeli <reduzent at gmail.com>
> > On Fre, 2018-02-02 at 18:31 +0000, Dario Sanfilippo wrote:
> > > There's an implementation of a peak holder in this blog
> > post: http://
> > > dariosanfilippo.tumblr.com/post/162523174771/lookahead-limiting-
> > in-
> > > pure-data. I remember testing it but please let me know if you
> > find a
> > > bug.
> > Very nice write up. Thanks for sharing.
> > > The current peak is replaced to whatever the input is after a
> > desired
> > > time, and the counter is reset whenever a new peak is found. It
> > > should be easy to change it so that the peak is reset
> > periodically.
> > It's not exactly equivalent with what I've asked, since your
> > implementation only takes new peaks into account after the hold
> > period
> > has ended.
> Perhaps my wording in the previous email was confusing: what happens
> is that every new peak will update the output immediately, and
> whenever that happens the countdown starts so that, should no other
> peak be detected after that time, the output will be set to whatever
> the input is in that moment.
> > Assume an input signal consisting of a series of 1-sample
> > impulses with a period that is slightly lower than the hold period.
> > The
> > output signal has a gap before each second impulse. For the use
> > case in
> > your article (which is also the use case I'm interested in), that
> > doesn't matter much, because the peak holder signal is fed to a
> > peak
> > enveloper which somewhat masks those gaps.
> In that case, we should expect a full-amp DC out of the peak holder
> for the impulses are faster than the hold time, and that's what we
> actually get:
Yes, correct. If the peaks reach the same level or are higher than the
ones before, then the hold period is prolonged. But when they have less
amplitude than the ones before, gaps appear. See:
With a true max(x[0-(-N)], a downward stairway would appear and there
wouldn't be any gaps.
As I said, that is only small difference and for the purpose of a look-
ahead limiter it probably doesn't matter that much.
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