What does Jitter sound like?

The reason I mention comparison between speed fluctuations in TT & digital jitter in CDP is because I experience these phenomena quite differently. As the speed stability of my TT has improved through various upgrades, I hear improved dimensionality, soundstage, bass control, dynamics, liveliness, focus, etc., even though pitch remains audibly imperfect. On this narrow point of pitch stability the CDP surpasses and I suspect will always surpass the TT (as evidenced particularly with piano music.) But somehow the ear is forgiving of even quite audible fluctuations in timing that originate in the analog domain. Perhaps this is because the physical locus of the stylus ensures that timing variations are applied uniformly across all spectra at each point in the LP groove.

In contrast, digital jitter seems to smear timing quite differently and more objectionably so. Having progressed through four generations of clock in my CDP I can say that most of what listeners think is synthetic & irritating about RBCD relates to jitter.

digital jitter seems to smear timing quite differently and more objectionably so. Having progressed through four generations of clock in my CDP I can say that most of what listeners think is synthetic & irritating about RBCD relates to jitter.

Jitter has absolutely no effect on the timing of audio signals....you are misinformed. I suggest you read the book I referenced above rather than make conjecture. Jitter creates side bands or frequencies that are not in the original music - the closest thing to jitter would be IMD distortion - the side bands if big enough and far enough away from the main signal frequency (so as not to be masked) will be audible as non musical related distortion or a higher noise floor.

As far as jitter affecting timing in what you hear - this is impossible unless you are a super bat (I don't even think bats are that good)? Jitter is in the nanosecond and faster range of timing. No human has shown the ability to sense timing delays in this range... in this amount of time sound travels 11 millionths of a foot...there is just no way hearing is that good. Besides - the output filter in the CD players DAC removes frequencies above 22 Khz anyway....so any effect cannot be related to "timing" even if you describe it that way.

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