Transcribing Tip - My Process
This is my process...
1) Transcribe everything at full tempo, without picking up the harmonica.
2) Slow the music down moderately (around 15-20%) and proofread my transcription carefully as I listen. This is very handy, I'll inevitably find little fixes (such as dips, slurs, pulls that were very soft, etc.).
3) If it's a very fast song, I'll do this again at around 40% slow.
4) As a last quick check I'll grab my harmonica and play along, making sure to read and play the rhythms I wrote, not what I remember hearing (it's easy to get swayed into matching what you're hearing and not actually play your notated rhythms).
This is my process, but most likely it won't be yours. I've been doing this for a long time, so I don't need to use a harmonica while transcribing, but you'll be checking every note you write by trying to match it to your harmonica. Take a listen to the first four bars of Little Walter's "Rocker" and we'll start walking through the process together over this series.