On 22/07/2018 03:50, Jason wrote:
In article ,
says...
If you ever find a CD drive raw output that feeds the electronics a
constant sample rate of 44,100Hz, I'll probably faint with shock.
Just a guess.. could the variation be caused by error
correction occurring? The errors might be on the disc or
induced by less-than-superb mechanics in the player.
Reading CDs is an analogue, mechanical process. The disc does not spin
at a uniform rate, but changes speed as it is read, both deliberately
and due to feedback and mechanical errors in the control circuitry and
motor. While the output of the phase detector is supposed to be either
on or off, dirt on the disc or using dye based writeable discs causes it
to vary, so threshold comparison is the order of the day.
The error correction introduces a delay in the chain from laser to DAC
input.
This is why the electronics has a buffer, so that the DAC and error
correction circuitry can be fed clean digits at a known clock rate and
output a clean signal at the right speed.
--
Tciao for Now!
John.