[chuck-users] How can I filter silence?

[Graham Coleman]

My pleasure, thanks for the ideas.

I enjoy this forum a lot. It is a supportive and positive an atmosphere
that encourages all- created by developers and users alike.

Excelcior!

On Mon, 25 Sep 2006, Jim Hinds wrote:

> Kas, Graham!
>
> Ya gotta love the way you think out of the box.  Break the rules to
> make better ones!  Thanks for the comments, code and inspiration.
>
> Jim
> ---"I dream of cheese, It's toasted, mostly"  Ben Gunn, Treasure Island.
>
> On Sep 24, 2006, at 8:55 09PM, Graham Coleman <gc at gehennom.net> wrote:
>
> >
> > From: Graham Coleman <gc at gehennom.net>
> > Date: September 24, 2006 9:50:44 AM HST
> > To: ChucK Users Mailing List <chuck-users at lists.cs.princeton.edu>
> > Cc: jahbin at romatictrances.com
> > Subject: Re: [chuck-users] How can I filter silence?
> > Reply-To: ChucK Users Mailing List <chuck-
> > users at lists.cs.princeton.edu>
> >
> >
> > I came up with some cheesy code to implement the idea.
> > It speeds up the tape when it hits silence. You'll need to
> > tune the time constants and the threshold for best results:
> >
> > sndbuf buf => dac;
> > buf.read("speak/wave.wav");
> > buf.pos( 0 );
> >
> > 0.05 => float tresh;
> > 0.01 => float rt; //release const
> > 0.4 => float at; //attack const
> > float xd;
> >
> > while(true) {
> >
> >   math.fabs( buf.last() )-xd => float a; //amp diff
> >   if ( a < 0 ) 0=>a; //non-negative
> >   xd*(1-rt)+at*a => xd; //the attack/release exponential filter
> >
> >   if ( xd<tresh ) {
> >     buf.pos( buf.pos()+6 ); //skip ahead
> >   }
> >
> >   1::samp=>now;
> > }
> >
> > To compute the time constants, use this formula:
> > //AT = 1 - e ^ (-2.2T/t<AT)
> >
> > or this if t is in samples:
> >
> > time const = 1.0 - exp( -2.2 / t );
> >
> > best,
> >
> > Graham
> >
> > On Sun, 24 Sep 2006, Graham Coleman wrote:
> >
> >> I'm not sure if there's anything in chuck that will currently do
> >> this,
> >> but I think you could write something like a noise gate, that
> >> tracks the
> >> amplitude of samples coming from a SndBuf and skips ahead until
> >> the level
> >> rises above a threshold.
> >>
> >> Not sure how well this would run in real time.
> >>
> >> Better, would be something that preprocesses the file with in/out
> >> points
> >> so the skips are quick.
> >>
> >> Graham
> >>
> >> On Sun, 24 Sep 2006, Jim Hinds wrote:
> >>
> >>> I want to scan some audio for dropped out sections.  It's long and
> >>> talky with 'significant' pauses between question and answers.  These
> >>> sections are filled with background noise, and often several seconds
> >>> long.  I'd like to shorten these empty sections (there are a lot of
> >>> them).
> >>>
> >>> I'd like to keep the files more or less intact (not sliced up into a
> >>> zillion intermediate files)
> >>>
> >>> Is there a unit in chuck that will be able to delete samples as they
> >>> pass through?
> >>>
> >>> Jim
> >>> _______________________________________________
> >>> chuck-users mailing list
> >>> chuck-users at lists.cs.princeton.edu
> >>> https://lists.cs.princeton.edu/mailman/listinfo/chuck-users
> >>>
> >> _______________________________________________
> >> chuck-users mailing list
> >> chuck-users at lists.cs.princeton.edu
> >> https://lists.cs.princeton.edu/mailman/listinfo/chuck-users
> >>
> >
> >
> >
> >
> > From: Kassen <signal.automatique at gmail.com>
> > Date: September 24, 2006 10:23:58 AM HST
> > To: "ChucK Users Mailing List" <chuck-users at lists.cs.princeton.edu>
> > Subject: Re: [chuck-users] How can I filter silence?
> > Reply-To: ChucK Users Mailing List <chuck-
> > users at lists.cs.princeton.edu>
> >
> >
> >
> >
> > On 9/24/06, Graham Coleman <gc at gehennom.net> wrote:
> > I'm not sure if there's anything in chuck that will currently do this,
> > but I think you could write something like a noise gate, that
> > tracks the
> > amplitude of samples coming from a SndBuf and skips ahead until the
> > level
> > rises above a threshold.
> >
> > Not sure how well this would run in real time.
> >
> > Better, would be something that preprocesses the file with in/out
> > points
> > so the skips are quick.
> >
> >
> > But.... It doesn't look like it needs to be realtime.
> >
> > I'd think about playing the file once and storing the sample
> > locations where the volume drops below a treshold (as well as the
> > ones where it comes back) in a array, then playing it a second time
> > and skipping those sections while writing the results to a new
> > file. in "silent" mode this should be doable faster then realtime.
> >
> > You could also make a array of the length of the file (in samples)
> > and only write buf.last() => array[sample++] as long as it's over
> > the treshold. Once the buffer reaches it's end you'd playback the
> > array again and record that, taking care to stop after the highest
> > value that "sample" got to in the first pass. This would be CPU
> > intesive but it's quite clean as a method, I think.
> >
> > It all stands or falls with the quality of the envelope follower.
> >
> > I've been thinking about doing something similar to the first
> > option and pre-scanning wavefiles for positive zero-crossings and
> > storing those in a array. This would take extra time when loading a
> > file but from then on you could do very clean loops, for example to
> > loop just a few cycles. I wonder how samplers that have a "snap to
> > zero crossings" setting do this. It might still be quite tricky
> > because not all samplers that do this do it all that well....
> >
> > Hope that's of some use.
> > Kas.
> >
>
>