Re: [linux-audio-dev] Final Scratch, custom kernel?

"rising" means amplitude ramps up as time goes forward, then drops down to zero. If you detect that the waveform is jumping from zero then ramping down, you know that the record is spinning backwards. Counting time between peaks gives the rate. This is good enough to track relative position through rate and direction changes. If you want to be able to pick up the needle and move it, you'd need an idea of the absolute position in the record. Probably, you'd have a stereo saw tooth pattern where the phase between left and right channels went from in phase to 1/2 cycle out of phase over the course of the entire record. Then, the difference between peak locations in left and right channels, or the difference in instantaneous amplitude between left and right channels will tell you where you are in the record. This is important because dj's pick up the needle and move it to a different part of the song while cueing. I was mostly thinking about detecting the needle-up when the waveform disappears, and needle-down when the waveform reappears. Then the apps could handle the needle-up case however they wanted... go silent like vinyl, or keep playing until the next needle-down, etc. -geoff