About jitter in a cd player

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gaetan8888

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#1
Hello

In the CD-77 Abbingdon Music Research web page from Thorsten Loesch, they say;

Why do you not specify jitter using the common (ppm) "parts per million" reference?

CD clock crystals are often promoted using a measure that specifies the difference of the actual frequency from the nominal frequency, usually specified as the deviation in ppm (parts per million). It should be noted that this specification has no bearing whatsoever on the jitter in CD players as it is a purely static measurement.

Phase noise in the clock is the primary cause of jitter. No reliable and standardised protocol exists to measure and specify jitter in a form that makes measurements comparable. AMR as a result, has chosen not to publish a specific number that would not be reliably comparable to the numbers published by others. Rest assured that the CD-77 offers one of the lowest levels of phase noise of any CD player produced.
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I found that interesting, but is it true, what can we say more about it ?

Thank

Gaetan
 
#2
Hello

In an article from Robert Harley in stereophile.com, I found a good definition of jitter.

http://www.stereophile.com/features/368/index.html

In the last page;
When we hear the effects of jitter, we're hearing voltage errors at the DAC's analog output caused by word-clock timing variations. This magnitude of the voltage error is a function of the signal amplitude and the jitter. Although low-level signals introduce more jitter in the interface, we're less likely to hear jitter on low-level signals. The voltage error may be on the order of a few microvolts with a low-level signal, but several millivolts with a high-level signal. Consequently, the audibility of jitter will vary greatly with the music's spectral content, level, and dynamics. According to HDCD® developer Pacific Microsonics—who has done extensive research into jitter audibility—the jitter's frequency and spectral distribution largely determine a transport's sonic signature. Jitter at one frequency may produce a certain sonic characteristic, while jitter at another frequency will create a very different subjective effect.

Clearly, jitter in the data stream driving a digital processor is audible—and a significant contributor to "digital sound." Because jitter adds artifacts we associate with digital audio in general, reducing jitter is an important step toward truly musical digital reproduction.—Robert Harley
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Gaetan
 
#3
Jitter is phase noise. It has spectral distribution in time domain just as amplitude noise has in amplitude domain. As such, it is measurable. The correct measurement is not a single value (that would be RMS jitter), but a spectral graph. If every maker published that graph, they would be surely comparable.
 
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