What does Jitter sound like?

Bigamp - Sooner or later the folks that dont understand the jitter thing will hear it or they will eventually upgrade their systems to the point where they hear it. Until then, it is like trying to explain how the earth looks from space.

Jitter is simply inaccuracies in the timing of the bits that make up the data stream. It is like a clock that ticks every second. If the clock ticks at exactly each second time interval, then it is said to have no jitter. If some ticks come at .999 seconds and others at 1.001 seconds, then the overall time will be accurate over many seconds, but there is jitter in the timing. This is how actual real-time systems work. They all have some amount of jitter.

The effect of this jitter on the D/A conversion is to create frequency modulation in the analog output. This means that the point at which the top of the cymbol crash was supposed to occur actually occurs maybe 1 nanosecond later and then the trailing ringing of the cymbol comes maybe 1 nsec earlier. The rate of this change can be anywhere from 10hZ to 100kHz or higher. If there is only one sample that occurs at the wrong time, it will never be heard, but typical jitter signature is usually a constantly changing time error. This is why it is audible. The brain detects these things just like it detects moving objects with eyesight.

The time error has both amplitude and frequency or spectra characterisitics. Each CD player or computer audio device has different amplitude and spectra for its jitter, so they can sound very different from each other, even though the data is always the same. Data errors are very uncommon for both CD players and computer audio. Jitter is the difference that you are hearing, if you hear a difference.

Steve N.
Empirical Audio

Audioengr,

From either a theoretical or experiential perspective, do you think the phomenenon of speed instability in a turntable is similar to digital jitter?

Shadorne - you are missing the point.

I may have missed something but I think we agree apart from your claim "the positions of the pits in the CD are a form of timing information that can cause jitter as they are read", which is incorrect.

My point was that there is no jitter added or lost by copying CD-R's many times (provided everything remains in the digital domain). The same is true for digital processing - it adds no jitter. ONLY a jittery clock or jittery signal makes jitter. If A CD-R somehow makes life easier for a CD player such that somehow the CD players clock runs less jittery then it will play with less jitter (but this may linked to how warped the CD is or how well centered the hole in the CD rather than "timing from pit spacing", IMHO)

Stereophile test CD # 2 contains an example of jitter. Based on that example, jitter is very, very bad and you don't want it! One would have to wonder if that might not be the largest contributer to listener fatigue in digital systems. Dgarretson's first post above is an apt description of what you hear in the test CD example.

Dgarretson - Wow and flutter exhibit the same results as jitter, frequency modulation, so the answer is yes, although some jitter occurs at rates and changes in ways that a turntable could not physically do.

Steve N.