Subject: [linux-audio-dev] How hard is it to write a pitch shifter?
From: Earle (earle_AT_ezi123.com)
Date: Wed Apr 07 2004 - 07:29:25 EEST
Im new to audio dev and to linux and am using SoundTracker as my Fruiyloops
replacement. I have done a _little_ bit of dsp programming, but really want
to learn more - hence this question!
I love trackers, and use them to nut out ideas. I record loops in to
soundtracker from my record player, and if it works in the song then I
record them agin with Rezound to do necessary processing from there.
But ST doesnt support plugins, and I need to be able to do a "quick and
dirty" pitchshift on the samples to see if it's gunna fit musically in the
track.
I tracked down a bit of code in ST that does a simple fade of the currently
selected data. I want to change this to do a basic pitchshift.
p = current_sample->sample.data;
p += ss;
for(i = 0; i < se - ss; i++) { //ss = selection start, se= selection
end.
double q = *p;
q *= THE PITCH SHIFTED SAMPLE MAGIC!
*p++ = CLAMP((int)q, -32768, +32767);
}
I found and implemented this bit of code for resampling, which changes the
pitch, but also the time
for(i=0; i <= MaxSamples; i++) {
processed_buf[i]= unprocessed_buf[(int) j];
j = j + pitch;
if (j > MaxSamples) break;
}
But I cant find out how to deal with the missing data that is removed - to
keep the original length. Is there a (n easy) way to do this? I really dont
care too much about artifacts as it is just to get an idea of the loop at
that pitch. or should I skip pitchshifters until I learn the basics?!
This archive was generated by hypermail 2b28 : Wed Apr 07 2004 - 07:30:16 EEST