Re: [Audacity-devel] Fwd: [Audacity-quality] Fwd: [Mixxx-devel] Using librubberband for tempo and pitch stretching.

[Gale A. <ga...@au...>]

| From Richard Ash <ri...@au...> 
| Sat, 22 Jun 2013 22:05:54 +0100
| Subject: [Audacity-devel] Fwd: [Audacity-quality] Fwd: [Mixxx-devel] Using librubberband for tempo and pitch stretching.
> On Thu, 20 Jun 2013 14:58:47 -0700
> Vaughan Johnson <va...@au...> wrote:
> 
> > Hi. I didn't get any response on this on -quality, but do any devs
> > know about librubberband?
> No, sorry - never (knowingly) used anything that uses it.
> 
> Worth pointing out we are I think at least one version behind on
> Soundtouch these days.

I feel - given we now have Sliding Time Scale and PaulStretch
for more extreme stretch - that the main issue we have with
SoundTouch is the length changes.

From some off lists I had with Olli (the SoundTouch author)
then Steve a while ago, there is no prospect of SoundTouch 
"fixing" the length problem because the emphasis of the library
is running it on complete files, not modifying short selections
where the proportional length change can be dramatic. 

We could perhaps "fix" it by inputting more samples then 
trimming - or repeating samples at the end to fit. But as 
Steve pointed out these changes would affect Preview 
globally, so probably not what we want.  

There are some worthwhile quality improvements in the 
latest SoundTouch library though. 

From the librubberband docs:
http://breakfastquay.com/rubberband/technical.html

 "sample-accurate stretching when run offline"

"Rubber Band implements pitch-shifting using the standard 
 technique of resampling before or after a time stretch, with
 the combination of resampling in one direction and stretching 
 in the other resulting in  returning the audio to its original
 duration but with different pitch.  This method has the
 advantage of making the amount of pitch adjustment extremely 
 accurate and stable, even for small changes."




Gale