I had some old taped original music recorded on cassette using an old TASCAM Portastudio, which was recorded at double the normal tape speed for cassettes (3-3/4 ips rather than 1.-7/8 ips, I believe) and really wanted to listen to them again and transcribe the music. However I only had a standard cassette player. So when I played them back, not only did I get only 2 of the 4 tracks on each side (since the Portastudio also recoded 4 tracks in one direction as opposed to the standard 2 stereo tracks on both sides of the cassette going in different directions), but I also ended up getting a half-speed version of the music; everything dropped by an octave and playing twice as slow as the original. Not a very pleasant listening experience.
Having an arsenal of software available to me now in my studio, I jumped right to my favorites - Digital Performer 8, and Logic Pro, thinking they could easily speed things up and get things right. But oddly, as powerful as these DAWS are, I could not find an acceptable way to do this. These products excel at being able to repitch without tempo change or tempo change without changing pitch, but when it came to just doing real-world speed doubling (doubling the tempt AND the pitch) either I could not do it or the artifacts introduced by the process were unacceptable.
Then I tried Ableton Live. And lo and behold it could not have been simpler or the results cleaner.
First record the cassette stereo output as a plain stereo audio track. Double click it to edit the sample, and in the Sample control box at the bottom of the screen, click the Warp button, then select the Re-Pitch option and halve the BPM (from 120 to 60). Voila! Now just save the auto using the Export Audio function (setting duration, formats, etc as you wish). It's a super-clean fast process.
To add in the other 2 stereo tracks as the original tracks 3 & 4 from the Portastudio, repeat the process, recording the backwards-sounding, slow original cassette audio to another audio track. Reverse the entire track, (the Rev button in the Sample control box) and do the Warp/Re-Pitch trick on that. You then have to manually align the tracks to start together as they originally did - this may be best done by taking the two adjusted exported audio files from Live back into your big ol DAW. And there is one other little gotcha… unless you have a super-speed-accurate cassette deck, there might be minor playback duration differences between the two sets of audio, since they are played back on hardware analog equipment as two physically separate passes of the tape. You may have to snip and slide things a bit (or stretch a track if you don't mind the artifacts it introduces) to get them to line up properly from start to finish, and timing might even vary a bit within each track. But at least you will have something workable to put back into your DAW as a basis for transcribing, re-recording, embellishing, whatever.
