ways of measuring acceleration of an endless encoder.

Working on some stuff meant to be controlled with endless encoders (basically an audio scrubbing setup), and was wondering if any one had any bright ideas on measuring the speed of the rotation and influencing the increment/decrement rate based on that value.

I have some knobs that out put a 1 when turned clockwise and a -1 when turned counterclockwise. I will then scale these to (presumably) sample indexes of a buffer. They work fine as I have them set up, with a constant increment/decrement rate, but I'd like to modify that rate based on how fast I am turning the dial.

I was thinking about measuring the amount of +1's or -1's I get during a specified period and adjusting the rate according to that, but I'd love to hear any other approaches.

Sorry no patch :)