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Here's one clue about whatever is causing the low quality speech. Speech sounds terrible at 1.01X faster, and it sounds excellent at normal speed (1.0X). So, the main problem is something that breaks with any change in frame size in the decoder. Any idea what that might be? Thanks, Bill On Tue, Oct 19, 2010 at 5:14 PM, Bill Cox <waywardgeek at gmail.com> wrote: > I was able to

...t to sound smooth, the resulting pitch > shift is horrible. You really need to use a transform that alters speed > smoothly, while maintaining the original pitch of the voice. If you look > in my spandsp library you will find a module which does exactly this, > using an algorithm called PICOLA. You can speed up or slow down a voice > in fine speed steps using this module, and the resulting voice is almost > the same quality as the original. There is a test program for it, which > should function as an example of how you need to call the library to > initialise and use it. &gt...

...if you can get it to sound smooth, the resulting pitch shift is horrible. You really need to use a transform that alters speed smoothly, while maintaining the original pitch of the voice. If you look in my spandsp library you will find a module which does exactly this, using an algorithm called PICOLA. You can speed up or slow down a voice in fine speed steps using this module, and the resulting voice is almost the same quality as the original. There is a test program for it, which should function as an example of how you need to call the library to initialise and use it. Steve On 10/20/2...

You're asking the wrong question. The question is not "why does it would bad with Speex?", but "why does it sound good with LPC10 and MELP?". And the answer is that both are vocoders. Try dropping frames/subframes with anything else (Vorbis, MP3, G.729, u-law, ...) and it'll sound terrible as well. The only reason it sounds good with vocoders is because the