(Oops, and this was meant to be in the earlier thread, in response to iamnycellist's question. Sorry, I'm obviously not paying enough attention.)
The video I mentioned before, with exercises that I worked with my teacher on, about 5 years ago, is a double DVD from Simon Fischer - The Secrets of Tone Production.
Simon Fischer, so I gather, writes (wrote?) a regular feature for The Strad magazine called The Basics.
The DVD describes in detail a set of exercises designed to get one to produce best tone that can possibly be obtained from a particular instrument by optimizing the pressure/speed combination for a set of five individual sound points. From there, one learns to vary each of the individual factors, first separately, and then in combination.
The exercises are conceptually simple and the exercises are nothing new. Leopold Mozart recommended this sort of thing 200-some years. The DVD is meant for players of violin, viola, cello, or string bass.
The full DVD is about 4 hours long, but the subject matter is about only six or so "simple" exercises. Why so long? The DVD shows kid after kid, for all of the four instruments, being taught the exercise and then performing the exercise, but not quite right. Fischer corrects the student until the student gets it.
The showing of how a player can do it wrong, then being corrected and doing it right, does require viewer patience and takes a while to watch, but to my mind, it makes the video especially valuable. As my Educational Psychology prof hammered into me, way back when, a student doesn't understand a concept until that student knows everything that is not that concept.
But even as good as the DVD set is, my teacher found things I did not do quite right. Also, she had an extra spin on tone production, not discussed by Fischer, that I have incorporated into my own understanding of the sound point/pressure/speed tri-relationship.
I get that some teachers are adamantly opposed to the video learning thing. Yeah, yeah, yeah. Students must do what students must do.