dhergert, very good points and questions. In jazz, even when you are looking at a chart and reading, you are still 99% improvising. Unless there is a specific bass part written out, then you are improvising on the song form and chord changes. It is just a map to follow. Many times when you do a session with a big band or orchestra etc. they will be arrangements that were written by an arranger specifically for each instrument. The bass parts can be written out note for note through the entire arrangement because that is what the arranger wants to hear, those very specific notes. Or, it can be a mixture of specific notes that he wanted to hear at certain sections of the songs so you will read the notes they want, or you might just get a chart of chord changes and the rest is up to you.
The end result is what is most important and I guarantee you that when you listen to the end result you might not hear any difference except if there is a melody line or specific figure that the bass plays.
At times, because of what jazz is, that map can be complicated with many chord changes per bar and interesting form sections to follow. Sometimes those chart can take a very long time to learn and memorize, and sometimes those charts are just given to you at the gig with no advance preparation. I agree that for some having charts can be a security blanket. If that's what those players need then God bless them, that's what they need. If their performance is better because of that then it should not matter as I always say the music comes first.
A big difference in jazz is that there are so many great classic recordings of jazz standards. Many are similar in nature and some are quite different. That to me is the beauty of jazz, you make it your own. You re-harmonize the chord changes, change the tempo, time signature, vibe, feel, etc. Instead of replicating what was done in the past, even if it has historical significance, in jazz most pay respect to the classics by making it their own. On my LaFaro album for the most part I kept everything pretty much like the originals because hey if it ain't broken don't fix it! But, I completely changed the approach to the classic Bill Evans song "Waltz for Debby". I did it as a bossa in 4 instead of a waltz in 3. That is a good example of taking a classic and making it your own and still honoring the beauty of the song. I am far from a harmonic genius, trust me, but I also made one very small chord change on my version of Cantaloupe Island on my "Downright Upright" album. There are 4 bars of D sus or D something on the original, don't remember actually! What I did was change the second D to a Db7 or sometimes we play a Db Major 7 for two bars. Let me tell you that a very little change like that makes a huge difference and to much of my amazement was heard around the world, because people are playing it that way now. They call it the Bromberg version, nuts! The point is in jazz it is expected to make things your own and to put your thing on the music, even if it is a very small change that gives the song an identity associated to you. Sorry for the stream of thought long response, but even if someone is reading a chart they are still mainly improvising from note one using the chart as a road map.
