Re: [Audacity-devel] Change Tempo algorithm

[Vaughan J. <va...@au...>]

Sorry I couldn't get back to you sooner, Mark. I can't replicate what 
you're seeing. I tried a 3-second test, selected it from 0.95s to 2.05, 
did Change Tempo -50%, and the result still starts at 0.95s.

I think it's a bug that the selection no longer changes to match the new 
length, as I think it did when we first wrote it. I hadn't noticed that. 
Anybody, was that on purpose, or just missed when the selection 
capabilities changed?

Anyway, it does all stretch to the right.

This isn't really a matter of what Soundtouch does. See 
EffectSoundTouch::ProcessOne and note line 189:
   track->Paste(mCurT0, outputTrack);

And mCurT0 was set to the beginning of the selection. So, we're pasting 
the new-length outputTrack beginning at the same point, ergo extra 
length is all to the right.

Don't know what's going on with your images. Can you replicate it and 
give the procedure, and SelectionBar numbers instead of images?

- Vaughan


Mark D wrote:
> Hey folks,
>
> I've been working on adding support for Change Tempo/Pitch to my label 
> shifting project for SoC. My lack of audio knowledge is rearing its 
> head again, so I figured I'd ask. When you use Change Speed, it only 
> stretches the waveform to the right, so the starting point remains the 
> same. Unfortunately, that's not the case for Change Tempo; here're 
> some pictures:
>
> Before: http://i37.tinypic.com/2s7b2og.jpg
> After: http://i35.tinypic.com/14jrdvk.jpg
>
> Could anyone shed some light on how the SoundTouch algorithms work, 
> because I honestly can't understand it too well. I've been using the 
> original length of the track compared to the final length of the track 
> to figure out what I should be doing with the labels (basically 
> mirroring the ChangeSpeed algorithm), but it seems like I won't be 
> able to do the same thing with this.
>
> Thanks a lot,
> -- 
> Mark
>