"Isn't the buffer in a CD player designed to store data so that it can be processed/decoded to extract the relevant audio bit stream information so that only these "bits" can be sent to the output of the DAC?"
There is minimal buffering in most CD players, usually inside a controller chip that does the servo control to control the speed of the spindle. There is also a CODEC that decodes the data stream from the Pits, as well as read amplifiers etc..
"Aren't CD data (pits) stored in an error correction format called Solomon-Reed interleave code (not a straight audio bit stream) and therefore the clocking of data from the lazer pick up off the disc is NOT directly related to the clock that clocks data in to the DAC output?"
This is true, the frequencies are not identical, but related.
"Isn't there a separate timing required to control the buffer under-flow or over-flow (not clocked by the same clock that controls the DAC output even if the timing is obviously related as the buffer is ultimately suppling the bit stream)?"
The clock for this is created by PLL, so no overflow or underflow occurs. The Crystal oscillator sets the frequency for the spindle rotation, but there is "slop" in the frequency of the clock due to the PLL. The spindle rotation is not that precise, and the bits coming off the disk have a lot of jitter, so it must track this. There is generally a buffer that attempts to do a second PLL on this and reduce jitter, but it is usually not immune to the jitter coming off the disk.
"Since the buffer "buffers digital bits" then we don't have potential for jitter UNTIL the clocking out in the output of the DAC - or am I missing something again? In which case how does the buffer PLL affect jitter - is it induced noise on the power rails or some other in direct manner?
The secondary buffer output is clocked by a divided-down clock based on the bit-density on the disk (CD versus DVD for instance). In theory it is a fixed clock and should not be subject to the jitter coming off the disk, but unfortunately all of them are. Somehow, the chips that are used for these processes are imperfect, or the power systems are imperfect, so some jitter leaks through. It seems like this problem should have been solved long ago, and it has probably gotten better, but the problem still persists.
All you have to do is rewrite a CD to CD-R and listen to it on ANY CD player and you will hear a difference in a resolving system. Put a mat on the commercial CD and play it and you will hear a difference. Put a treatment coating on the commercial CD and you will hear a difference.
If these CD mechanisms worked ideally, then none of the above treatments would change the sound.
Steve N.
Empirical Audio
There is minimal buffering in most CD players, usually inside a controller chip that does the servo control to control the speed of the spindle. There is also a CODEC that decodes the data stream from the Pits, as well as read amplifiers etc..
"Aren't CD data (pits) stored in an error correction format called Solomon-Reed interleave code (not a straight audio bit stream) and therefore the clocking of data from the lazer pick up off the disc is NOT directly related to the clock that clocks data in to the DAC output?"
This is true, the frequencies are not identical, but related.
"Isn't there a separate timing required to control the buffer under-flow or over-flow (not clocked by the same clock that controls the DAC output even if the timing is obviously related as the buffer is ultimately suppling the bit stream)?"
The clock for this is created by PLL, so no overflow or underflow occurs. The Crystal oscillator sets the frequency for the spindle rotation, but there is "slop" in the frequency of the clock due to the PLL. The spindle rotation is not that precise, and the bits coming off the disk have a lot of jitter, so it must track this. There is generally a buffer that attempts to do a second PLL on this and reduce jitter, but it is usually not immune to the jitter coming off the disk.
"Since the buffer "buffers digital bits" then we don't have potential for jitter UNTIL the clocking out in the output of the DAC - or am I missing something again? In which case how does the buffer PLL affect jitter - is it induced noise on the power rails or some other in direct manner?
The secondary buffer output is clocked by a divided-down clock based on the bit-density on the disk (CD versus DVD for instance). In theory it is a fixed clock and should not be subject to the jitter coming off the disk, but unfortunately all of them are. Somehow, the chips that are used for these processes are imperfect, or the power systems are imperfect, so some jitter leaks through. It seems like this problem should have been solved long ago, and it has probably gotten better, but the problem still persists.
All you have to do is rewrite a CD to CD-R and listen to it on ANY CD player and you will hear a difference in a resolving system. Put a mat on the commercial CD and play it and you will hear a difference. Put a treatment coating on the commercial CD and you will hear a difference.
If these CD mechanisms worked ideally, then none of the above treatments would change the sound.
Steve N.
Empirical Audio
