Simply put, Transcribe! is an amazing music software tool that allows you to take any standard audio file (mp3, wav, aif, & more), of a song, lick, solo, etc. which you're trying to master; and, among other things, slow it down to variable speeds without changing it's pitch, in order to make the transcribing or learning process so much easier.
Transcribe! has been around for some time, and chances are you either already have it or have heard about it. If you haven't, I'm happy to do some of the preliminaries and introductions. I highly recommend you make it's acquaintance, even if just casually.
At $39 US, the "bang for the buck" factor is phenomenal considering the number of features and uses it offers. You can download a 30 Day Free Trial version, after which you're required to purchase a license key in order to keep using it. Once you do purchase however, you never have to pay for another upgrade. I purchased mine in 2001, or thereabouts and whenever a new version comes out, I simply download it to my computer & it recognizes my license key automatically.
Besides the slow-down function, I get a kick out of the chord analyzer, which picks out the frequencies in a given wave form, and when possible according to instrumentation, spells out the name of the chord being played, including extensions. There's also a sophisticated EQ, with presets for blocking out or soloing different instruments, according to their frequency ranges.
You can also pitch shift with or without changing tempo.
It allows you to export either the whole or parts of a file to WAV, AIFF or mp4. This is very useful, if say, you have a phrase of 2 or 4 bars (or whatever length) that you wish to expand & jam to outside of Transcribe!. You can specify how many repetitions of the phrase you want exported, as well as the file format. You can then open it up for further use, editing or jamming in any sequencer, iTunes, etc.