This is far from being the first discussion of the nature of learning to improvise music. I believe in the past, we have agreed that improvising at its best is spontaneous composition. When we talk about jazz, we are talking about a form of music that is primarily less than a century old. Over that century, jazz has moved from Dixieland and blues, to bebop, to modal, to funk and now to whatever new variations there are. There are some good players who are so ensconced in the standard jazz culture, that they'll always end up playing some conventional jazz-blues things in music that needs something else. On the other end of the scale, there are players who will always play the most out there stuff in places where it cold have been standard. This is mostly a matter of taste, what they "heard" in their heads, but improvised.
Today, the need for music is not so much in the orchestra pit or the bar, but in videos or from DJs. Putting aside the issue of money and earning a living, just to play anywhere requires a different set of skills. Remember movie scores of the 1950's? Composers had their score played by an actual orchestra. Today, it's all synthetic, and more hip hop than Herrmann.
How does improvisation relate to this?
I think we should look at what will be wanted from now into the future. Aside from the music, it clear to me that anyone who wants to produce or be a part of music will need some extra-musical skills, like editing, mixing, exchanging music with distant collaborators, and sometimes the ability to expose their product on social media, or possibly, to sell it on the numerous Internet outlets.
What musical skills will be valuable from now onward?
Reading is a great thing for learning, and it is very important for preparing high-level jobs, such as touring with performers like Chick Corea, but also with locals who have a book. None of this is part of my world. I have never had a job that required reading skills beyond being able to follow a chord chart, but I've worked with many musicians who have. How many positions of that nature, paid or unpaid, are there out there now?
I'd conclude on "improvising by ear" by saying that it will likely be the most widely needed skill going forward, combined with the ability to virtually mingle on social networks, be generous and personable in the real world and possess at least some of the technical understanding I mentioned above. "Improvising by ear" might even be better defined as follows:
Improvising by ear: Using a sufficient understanding of the instrument and an awareness of the musical context and culture, the ability to comfortably play in any circumstance. This requires a sense that taking part in the organised sound of any size group is not solely a matter of playing the right notes in tune that relate to the harmony and rhythm, but also knowing when to play and when not to play and how many notes to play. One of the pitfalls of practicing with tracks is the lack of musical interplay with others. Because we spoke of improvisation, the full implications of improvising a solo often require the accompanists to also improvise their response to the soloist. Not all the time, as in New Orleans, but when it matters for rhythmic, melodic or harmonic support. When I think of great live performances, I think of what the others are doing when someone is improvising a solo.
Musical ear is more important the the eyes or the fingers. Exposing your ear to varied music and making a mental note of particular aspects of that music comprise the "interest" to build your "capital" of musical culture. Before anyone brings up Evelyn Glennie, we'll need to realize that the ear itself isn't the only organ that can hear, so by musical ear, we are not talking about the actual ear, but a construct that allows you to absorb music.