Linards Ticmanis wrote:
Michael J. Mahon wrote:By a happy coincidence, the period of the PWM pulses created by DAC522 is 46 Apple cycles, and your sampling scheme should reproduce its output perfectly!Well, RT.SYNTH is almost inaudible with it, so there must be *some* kind of problem...Wouldn't there be a high dependency of the output quality on just *where* in the 46-cycle DAC522 cycle each new 23-cycle emulator sample starts?
Each DAC522 pulse will span two 23-cycle samples, with what should be a stable phase relationship (assuming accurate cycle timing). Consider each pair of consecutive 44kHz samples to be a single 22kHz sample (which, by the time it goes through the reconstruction filter of the sound card, is the case). Then regardless of the relative phase of the sampling, each pair of samples will add to the same total (for the equivalent 22kHz sample). The result should be excellent after the low-passing of the speaker, ear, etc. Are you sure that the 44kHz samples are as you expect? Could you capture a few seconds as a .wav and email the file to me? It would be interesting to see what's going on. -michael Music synthesis for 8-bit Apple II's! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it is seriously underused."