Transcribing is a pretty huge topic to cover in just one reply...
but a few key elements to my process have included starting really simple... some of the first solos I transcribed were very minimal in terms of content and that was a key aspect of training my ear to hear that language. I would say transcribing entire solos early on helped me a lot in terms of looking at the shape of a solo and understanding tension and release. And then just hours and hours spent with that vocabulary I was taking from records, shedding it, and then trying to turn it into my own thing.
If you're interested in learning more about it, I have a whole series of transcription lessons on my video lesson website.
You can check out some free previews of the lessons here:
Video Bass Lessons with Janek Gwizdala*|*Not just bass lessons, but tools for your musical life
and if you sign the mailing list we'll actually send you a full length lesson for free.
And if you're interested in becoming a member you can check out the info here:
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Thanks,
Janek