I think this had been touched on before, but I haven't conquered it yet and am therefore still obsessing on it. Due to a couple of things; my 'Me and PC' experiments, and then happening across this bassist (via a link from BollBusters site); got me to thinking about pitch and how to perceive it to get what I want in terms of intonation as well and timbre. What the bassist above is guilty of, as am I, is playing flat. At least I think that's what it is. I've found that playing, while both acapulco and with others, is that if I play what seems sharp to me (at the time) that in an acapella thing that I tend not to wander flat out-of-key, and with others to nail pitches much more. Also, when I approach it like this the sound (timbre) seems to get real sparkly and more 'tenor sax' like rather than the awkward 'baritone sax/bass with a bow' kind of tone. Now, the difference that I'm talking of is incredibly slight. When I have the next note in my ear, I simply want to hear a 'bright' version of that note (pitchwise) and the effect is achieved. It is a little 'tiring' though, and for a long period of time I'll lose site of this sound. It's a matter of training, I guess. Has anybody else given this much thought?