Date: September 24, 2006 9:50:44 AM HST
Subject: Re: [chuck-users] How can I filter silence?
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
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Date: September 24, 2006 10:23:58 AM HST
Subject: Re: [chuck-users] How can I filter silence?
On 9/24/06, Graham Coleman <gc@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.