[Speex-dev] Increasing the speed of speex playback

Bill Cox waywardgeek at gmail.com
Tue Oct 19 14:14:49 PDT 2010

I was able to easily hack in an option to play back at different
speeds.  For example, using "speexdec --speed 2.0 file.enc file.wav"
plays back encoded file.enc at 2X speed.  What I did was divide
st->frameSize and st->subFrameSize by the speedup, and added a
SPEEX_SET_SPEED decoder control for the nb_celp decoder.  This
produced speech that was 2X faster than the original.

However, the quality is very poor.  This is where it gets harder for
me, as the quality is impacted by so many parts of the code.  Can
anyone guess which part of the decoder is leading to such poor quality
when I cut the frame size in half?  This hack works very well in
LPC10, and fairly well in MELPe.

I've attached two outputs from speex: the decoded playback at normal
speed, and the 2X speed version.

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