I use the “Change Tempo” effect. It keeps the pitch intact.
Does it manage to do its job without sounding like being recorded under water?
For practising purposes I often slow the tunes down to 50%, and an older version of Cool Edit Pro, Goldwave, Audacity etc. don’t manage very well at such extreme settings. They all slow down, and maintaines pitch, but details like ornaments are often lost. If a whistle is backed up by guitar, the trouble really starts.
I have found one piece of software that slows down/changes pitch very well: The amazing slowdowner at: http://www.ronimusic.com/amsldowin.htm
I checked audacity “change tempo” for the underwater effect. I do hear it at 50% slowed, but it wasn’t too bad, at least to me. At 30% slow down if felt fine. I’m using Audacity 1.3.3.
The Cool Edit Pro version I used is pretty old. The Goldwave version is recent, and the Audacity version was rather old too.
When trying out Amazing Slowdowner I was struck by the cleaness of the sound even slowed down at more than 50%.
Tunes with string instruments usually suffer the most, but even with strings the Amazing Slowdowner sound quite good at extreme settings.
What’s nice about it is that you can slow down tunes and/or change pitch both from files and CD’s.