R/E/P > Dan Lavry

Proper word clock implementation

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Lucas van der Mee:
The answers to those questions we have given several times before in this thread. But to make it easy for you and not have to search for it I’ll say it again:

Jitter at the converter chip will be lower, in most cases, when clocked to internal. There is no doubt about that, no mystery, we never claimed anything else. However, we do say a number of things that are beyond this question.
1.   Big Ben is an excellent solution if you need a master clock. It is low jitter and offers a lot of features the competition does not have.
2.   If you need to clock to a jittery source, for instance a SPDIF output of a computer or a commercial cd player, having the Big Ben re-clock the data first, will very often improve the sonic and MEASURABLE quality of the converter used. The amount of improvement is all dependent of the quality of the PLL circuit of said converter. In other words, the better the PLL, the least improvement will be noted.
3.   For this one I will be quoting Max, because he put it so well:

“Yes, Jitter is a deficiency that causes a certain type of distortion to the signal. However, the ear, being a non-linear device with respect to frequency, will not hear all jitter the same. It is very easy to create a scenario whereby two signals can be induced with jitter, one of which has significantly more jitter than the other, but sounds audibly more ACCURATE to the ear. The distortion due to jitter on the one with more jitter can be relegated to frequencies that are entirely out of the human audible spectrum in various ways, whereas the other can have far less jitter, but at frequencies that are much more audibly apparent.

It is certainly possible to design an external clock in such a way that the increased amount of jitter that results will have less of an audible impact than the internal clock by itself. For this reason one cannot claim that an internal clock will always be more accurate - merely that it will theoretically always have less jitter. There is a significant difference between the two, and the testimony we have been seeing on the market and in our own testing with respect to Big Ben over the last few years certainly attests to this.”

I would like to add to this: There are numerous examples in technology, where we find that an actual reduction in performance of one parameter can lead to a perceived and sometimes actual improvement, in others. A good example in audio is dither, (noise shaped especially). By adding dither we actually reduce the dynamic range, yet we improve the perceived noise floor by masking the annoying noise of rounding errors.

My last word on this topic is, people do perceive more than science can explain. Our senses are intrinsically subjective, however the more experienced we become, the more we train our perception, the more OBJECTIVE we can become and obviously, your mileage may vary.

Lucas van der Mee
Sr. Design Engineer
Apogee Electronics


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