Hi

just played around with three GPLed time stretching libraries and wanted
to share my (unscientific and subjective results)


RubberBand (Phase vocoder)
pro: fast, decent quality under non-extreme conditions, we can supply a
     frame map (which is important for avoiding cumulative errors)
con: bad quality under extreme conditions (multiply tempo with a factor
     of 0.33 or 10.0)


LibSBSMS (sinusoidal subband modeling)
pro: REALLY good quality, still REALLY good quality under extreme
     conditions, natively supports sliding tempi.
con: we can't supply a frame map, very slow (30 seconds need ~40 sec of
     processing on my 1.4GHzer)


SoundTouch (SOLA: basically finds zero-transients of your signal,
                  cuts your audio in small pieces, and glues them
                  together.)
pro: very fast
con: really bad quality under extreme conditions (sounds choppy), we
     can't supply a frame map



i'd conclude from this:
don't use SoundTouch (RubberBand is similarly fast and better quality).
Use RubberBand within MusE for timestretching
Maybe offer to use LibSBSMS for slow quality results, e.g. for a final
downmix.



if you want to try them out:
LibSBSMS and SoundTouch are used in audacity.
When you choose Effects -> Change Tempo, you're getting SoundTouch,
and when you choose Effects -> Sliding Tempo/Pitch Scale, you're getting
libSBSMS.
And RubberBand support will hopefully be in MusE soon :)

greetings
flo

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