That's a 160 ppm discrepancy, within the expected range for two unsynchronised crystal oscillators. It also has nothing to do with rotation. The disc motor is servo controlled to provide a reasonably constant readout rate. The data is then buffered, processed, and clocked out to the DAC by a crystal oscillator. You'll get similar results with any unsynchronised DAC/ADC pair.Unfortunately, the method does not work with CD players. The difference in rotation speed and thus resulting frequency makes Deltawave unable to work. With 1kHz dithered as an original signal, I get the stagecoach-wheel effect. From the player I get 999.84Hz. Funny.