davidsch, the clock determines each time when the recorded analog waveform is sampled, as well as the time at which each sample is played back to reproduce the original waveform. Any deviation from a regular period in either recording or playback is jitter and will result in distortion, but the distortion isn’t harmonic and the result can be more objectionable than harmonic distortion. Having a stable, quiet clock is important for recording and playback, but for playback we often have separate sources and DACs which each have their own clocks that have to remain synchronized through clock recovery.
