These wav files show how Sonic performs at increasing speech rates.  All sound
sampels are in the public domain.

sonic.wav
This is a sonic 2X sped-up version of a public domain librivox.org recording, from
the audiobook "Princess of Mars".

soundtouch.wav
This is the same recording as sonic.wav, but sped up using soundtouch, which
uses WSOLA rather than the sonic algorithm.  Even at 2X speed up, you should be
able to hear the characteristic WSOLA distortion relative to the sonic version.

talking.wav
This is my father talking, using a decent microphone and 44KHz sample rate.

talking_2x.wav
This is his voice sped up by 2X using Sonic.

espeak_s450.wav
Sonic also performs well at increasing the speed of synthesized speech.
espeak_s450.wav was generated using 'espeak -s450 -f test1.txt -w
espeak_s450.wav'.  This is the highest speed currently supported by espeak,
though Sonic can speed up espeak to much faster rates.

espeak_sonic.wav
This was generated with 'espeak -f test1.txt -w out.wav;
sonic 2.6 out.wav espeak_sonic.wav'.  Sonic sped it up 2.6X, which is about the
same speed as espeak at -s450.  I personally feel that the sonic sped up sample
sounds better than espeak at -s450.

twosineperiods.wav
This is just two sine periods, which is too short to hear.  However, it's
useful for making sure the flush function works correctly.  A 2-X speedup should
result in one sine period with no distortion.