Here’s a neat site that has a number of classic jazz solo recordings played back at half speed. It’s called Half Speed Jazz. The recordings aren’t really at half speed, they are retained at the original pitch. And then it’s played at the original speed.
Someone who isn’t a jazz improviser might wonder why recordings slowed down to half speed are helpful. Transcribing classic jazz solos is considered an essential part of learning to improvise well. Particularly when you’re a beginner at transcribing, it’s helpful to be able to slow down the recording to pick out individual notes.
While it’s much more convenient to simply get a hold of software that will do this for you, I found it interesting to take some time to listen to the slowed down recording and then the original speed. Different things about the solo stuck out to me, depending on which speed the playback was. It’s also striking how hard some of the solos swing at half speed.