Along those lines - what you want it to find a high quality time-scale shift algorithm. If you're batch processing samples offlines, I believe Audacity can do this base on a STFT that includes phase information. For fast online shifting, PICOLA, as provided by the SpanDSP library, might work well for you, although I haven't tried it at an 8x speedup.<br>
<br>Stuart<br><br><div class="gmail_quote">2010/10/19 Jean-Marc Valin <span dir="ltr"><<a href="mailto:Jean-Marc.Valin@usherbrooke.ca">Jean-Marc.Valin@usherbrooke.ca</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
You're asking the wrong question. The question is not "why does it<br>
would bad with Speex?", but "why does it sound good with LPC10 and<br>
MELP?". And the answer is that both are vocoders. Try dropping<br>
frames/subframes with anything else (Vorbis, MP3, G.729, u-law, ...)<br>
and it'll sound terrible as well. The only reason it sounds good with<br>
vocoders is because the codec parameters are in fact synthesizer<br>
parameters that don't have a direct connection with the signal.<br>
<br>
Jean-Marc<br>
<br>
Bill Cox <<a href="mailto:waywardgeek@gmail.com">waywardgeek@gmail.com</a>> a écrit :<br>
<div><div></div><div class="h5"><br>
> I was able to easily hack in an option to play back at different<br>
> speeds. For example, using "speexdec --speed 2.0 file.enc file.wav"<br>
> plays back encoded file.enc at 2X speed. What I did was divide<br>
> st->frameSize and st->subFrameSize by the speedup, and added a<br>
> SPEEX_SET_SPEED decoder control for the nb_celp decoder. This<br>
> produced speech that was 2X faster than the original.<br>
><br>
> However, the quality is very poor. This is where it gets harder for<br>
> me, as the quality is impacted by so many parts of the code. Can<br>
> anyone guess which part of the decoder is leading to such poor quality<br>
> when I cut the frame size in half? This hack works very well in<br>
> LPC10, and fairly well in MELPe.<br>
><br>
> I've attached two outputs from speex: the decoded playback at normal<br>
> speed, and the 2X speed version.<br>
><br>
> Thanks,<br>
> Bill<br>
><br>
<br>
<br>
<br>
</div></div><div><div></div><div class="h5">_______________________________________________<br>
Speex-dev mailing list<br>
<a href="mailto:Speex-dev@xiph.org">Speex-dev@xiph.org</a><br>
<a href="http://lists.xiph.org/mailman/listinfo/speex-dev" target="_blank">http://lists.xiph.org/mailman/listinfo/speex-dev</a><br>
</div></div></blockquote></div><br>