Rich, jitter in optical discs is real and affects sonic quality. The jitter is found in playback equipment and also the production process. You can have a player with very low jitter due to stability of the servo and transport, but if the disc was produced with poor jitter, sound quality will be affected. And vice versa. The laser generator and optical pickup are also prone to various effects.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated