Issue regarding the 'Sliding Time Scale/Pitch Shift' Effect

Audacity Help Forum Windows
1

First of all, I wanna thank the developers for this great programme. One of the most useful ones out there.

I installed Audacity 2.0.5 (via installer) on a Win7 64bit machine and I wanna
create a mix of some songs I am currently favouring.

We are talking mostly about ‘electro summer chillout’ ( or so :wink:) music, so the
tracks are pretty easy to mix as they all have track-wise constant BPM.
Where 2 tracks crossfade, I also adjust the tempo by using the Effect ‘Sliding
Time Scale/Pitch Shift’. It is almost perfect for my task and it creates sliding
tempo transitions of pretty descent quality.

However, when I apply the Effect to a section with a distinct bassline (which
is the case with almost every transition) the bass becomes kind of ‘shallow’.
It sounds as if the driving heights are being smoothed away or something
(can’t explain it any better), regardless of speeding it up or down and the
percenatge used. (I’ll attach a before/after example)

I figure it probably has something to do with the algorithm of the Effect
but I don’t really have a clue. Is there a way to prevent this unpleasant
side-effect from happening?

Any help is much appreciated, Thx.

2

“Time stretching” is difficult (algorithmically). There are several different approaches to the task including “synchronized overlap-add”, “Sub-band Sinusoidal Modelling”, “Phase vocoder” and others. None are perfect. The "Sliding Time Scale/Pitch Shift effect uses “Sub-band Sinusoidal Modelling” (SBSMS), which produces pretty good quality in most situations, but as you’ve noticed, it’s not perfect. For pure “quality”, resampling is the best by a long way, but has the major limitation that it changes both speed and pitch (see: http://manual.audacityteam.org/o/man/change_speed.html).