What does Jitter sound like?

Shadorne - how do you think the data coming off the disk is stored in a buffer in the CD player without a PLL?

BTW, I am an EE. I was a design team lead on the Pentium II at Intel Corp. 30 years design experience designing everything from big disk and tape controllers for IBM equipment to massively parallel supercomputers to slot 1 processors.

Steve N.
Empirical Audio

Shadorne - how do you think the data coming off the disk is stored in a buffer in the CD player without a PLL?

I'll take a stab at what I think is going on and you please correct me - I much appreciate your efforts/time to educate me. I apolgise if some of what I said is misleading - just trying toget my head round all this.

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?

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?

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)?

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?

If you have any suggestion for good books on this subject - let me know.

"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

I am skeptical about all this. To me, the biggest flaw is the sampling rate itself. A well recorded sacd can sound quite amazing even on a budget player with mediocre parts. The cd layer won't sound as good and is not as resolving with the same player. With all due respect Mr. Lessloss, removing a few pico seconds of jitter seems like polishing a turd. So what does jitter sound like? I am sure excessive jitter plays a role in masking detail to some extent but it sounds more like marketing hype backed up by "white papers".

Rotarius....THANK YOU!!

Over-clocked under-flow buffer bits blah blah blah blah...

The question was WHAT DOES JITTER SOUND LIKE, and the conversation degraded into a brain battle of engineers. If small amounts of jitter affected sound like small amounts of other distortions, then the above question would have a real answer such as could be given to the following questions:

What does mistracking sound like?
What does a ground-loop sound like?

These are things we can identify. Instead, we're arguing about whether we can even hear it or not, and the final answer (assuming it's something we actually can hear) seems to be "it sounds like less clarity." With an answer like that, you might as well be saying "ummmm... it just sounds worser."