It must be clear by now that the timely detection of a pit transition resulting in a digital 1 is a matter of critical scrutiny. Even the smallest deviation in detecting the
precise transition results in timing errors called jitter. Causes of jitter are many. It could be bad pressings where the pit walls aren’t perpendicular to the surface but crooked. Other optical problems prevent the laser beam to properly hit the reflective layer with the pit pattern through the polycarbonate. This could arise when a CD is still greasy from the stamping process. Other optical problems are the result of light scattering in the plastic layer rather than getting a clear lock. Wobbly or eccentric discs are also detrimental to correct data capture as the laser needs to physically adjust hundreds of times a minute to track the erratically spiraling pits. Poor power supply design compromises matters further as the laser’s motor power is diverted by other circuits. The large currents of the laser servo (which assists in tracking the pits) can interfere with the tiny response current in the optical read diodes. And so forth.
The upshot simply is utter confidence that calling the audio CD a mostly analog medium is correct. By the way, a
data CD for computer use
is truly digital by design. It operates with different error correction schemes and sports no spiral groove but is addressable directly to any given word and capable of re-reading certain sectors as needed. Is it any surprise then that the audio market is overrun by ‘after-market’ tools meant to adjust or correct the quality of audio CD data read-in?