[asterisk-dev] adjusting the playback speed of voicemail messages.

[Dan Mills]

On Thu, 2008-04-03 at 13:40 -0600, Michael Grigoni wrote:
> John Todd wrote:
> 
> <snip>
> 
> > I don't know 
> > enough about how JACK works to say what a filter would look like to 
> > slow down or speed up audio without distorting the pitch.  Let us 
> > know if this is the right solution, and the methods and details of 
> > any successful tests!

Jack just passes blocks of floating point samples around, what DSP is
done is entirely up to the jack applications.


> This thread got me to do a quick search for implementations of
> variable speech control (hopefully public domain or open source)
> but not much is out there.  

There are two open source libraries doing the constant pitch at variable
speed thing that I know of, Rubberband (written in C++) and
libsoundtouch which is in C. 

Both are fundamentally phase vocoders but they have different tradeoffs,
they both work and may be worth looking into. 

Regards, Dan.