I should preface this with the note that I'm running BiaB 2009.5, so things may be different with the 2010.5 version.

To test this out, I picked the PopLondon style, which is optimal at 65 BMP. I exported a piano track as a .WAV at 65 BPM, which sounded fine. I also exported a track at 60 BPM, which had noticeable artifacts: warbles, pre-echo - all the sorts of audio nastiness that is associated with time shifting.

I imported the two wave files into Audacity, a free audio editor. I selected the 60 BPM track and chose Effect | Change Tempo... to determine the length of the track (101.02 seconds). I then selected the same effect for the second track, changing the its length from 93.25 seconds to 101.02 seconds.

The result had many of the same audio "wobbly" pitch artifacts as BiaB. So Audacity was no better than BiaB.

Next, I imported the files into Reaper. After stretching the track 65 BMP track to the same length as the 60 BPM track, I tried various pitch shifters. I listened in playback mode, using Good (64 pt Sinc), so the actual results are potentially a bit better than what I heard. The results were varied:
  • SoundTouch was noticeably bad, with the same artifacts BiaB and Audacity had.
  • Dirac LE (slow) was (to my ears) essentially artifact free.
  • Low Quality Windowed (fast) had serious phasing issues.
  • elastique Pro had a slight warble in spots, and the piano sustain was a bit buzzy, but was very good.
  • elastique 2.1 Pro was (again, to my ears) essentially artifact free.

The elatique algorithm has a bazillion parameters to mess with, and I didn't really fiddle with any of them.

Shifting from 65 BPM to 60 BMP is quite a lot - 8% - and BiaB 2009.5's version isn't usable. Both Dirac LE and elastique 2.1 Pro produced results that were - to my ears - quite usable. Keep in mind that, the slower the tempo, the more pronounced small timing issues will become.

So if you need to create tracks at tempos below those suggested by the RealTracks, exporting the tracks as .WAV files and using another program to do time shifting may provide a viable option. It's certainly one I'll consider, because it's frustrating to have a song just a hair below the suggested tempo, and not be able to use a track.

Again, this was a very limited test, and YMMV. Still, it suggests that there might be better alternatives for PG Music to consider.

-- David Cuny
My virtual singer development blog

Vocal control, you say. Never heard of it. Is that some kind of ProTools thing?