My first encounter with Bessel functions was from a professor who in his youth had built digital amplifiers -- before dsps could switch at 44k Hertz. (From memo

My first encounter with Bessel functions was from a professor who in his youth had built digital amplifiers -- before dsps could switch at 44k Hertz. (From memory he had a 1k pwm) He did it by predicting the position of the magnet in the speaker coil by fitting a function over the last few known positions. Bessel functions are othogonal, and their Fourier transforms are the base polynomials band limited between -pi and pi. His argument was that by fitting a sum of Bessel functions to a sequence captured periodic signals. I've used this trick several times, and love the "what is this black magic" reaction I get when showing it to others. Guess the cat's out of the bag now...