When I was studying Jazz Bass at Bellarmine University in the 90s we?
There are several apps and programs that can help. Almost all DAW can slow down a tune maintaining their pitch and there are browser based solutions. I use Transcribe! (Exclamation mark theirs) Below is a screenshot of the window. I imported a MP3 (the soundwaves) and it automatically places the notes on a pianoroll (your mileage may vary) You can then loop, slow down and do a bunch of other stuff. It wasnt expensive at all.