What are the jazz notes? Seriously, what are the notes that distinguish jazz from other styles of music? What notes are different in jazz than the music of Mozart, or Bach? Is it the flat five, or the minor 3rd? Nope. Mozart used them and Bach did too. Heck, I am not incredibly versed on the motets of Machaut, but I am pretty sure you can find them in there just as well. So here is a simple truth - while many focus on the harmonic and melodic qualities of jazz, rhythm bares as much a part of its signature as any other aspect (If I were feeling more ambitious I might lay out the argument why rhythm is an even greater part of its signature than any other element- perhaps for a later blog). But here in lies the problem and solution. While many students focus on "getting the notes" to a transcription there may actually be more to gain by focusing on the rhythm alone.
Focusing on the specific rhythm of a player shifts the ear to different aspects of improvisation as well as the group dynamic. It also builds a players capacity to improvise with strong rhythmic ideas, which lends itself to a confidence which allows us to better deal with the harmonic aspects of soloing. The approach I suggest is to find a great one or two measure rhythm and use it as a template for your improvisation. Use that rhythm as a exercise and create harmonic ideas based on that rhythm. Or maybe zero in on an overriding concept, like beginning ideas on the and of four, or starting a phrase with an 8th note triplet. These are all aspects of the jazz language that as important to master as "the notes."
Focusing on the rhythm will have one additional advantage. Experienced transcribers will attest to this - notating the rhythm is harder than notating the pitch. On the most basic level, this music is from an aural tradition and not all of the ideas fit nicely on manuscript paper. Deciphering those ideas and bringing them into our traditional notation is hard. You will become a better musician by forcing yourself to deal with only the rhythmic aspect of a solo. It is challenge you to think about this music from a slighter different footing - and that new found foothold will make a big difference!