It has to do with the way the clock is extracted from the SPDIF signal. There is a high degree of correlation in it. This leads to a great deal of data-related artifacts in the recovered clock.
(If someone was to hook up some sort of listening doo-hickey to the point in the circuit where the PLL filter is, you will hear a very distorted version of the programme material.)
Any reflections in the data stream manifest themselves into a change in the data-dependent jitter. Not so much in the actual amount, but the frequency distribution. Absolute jitter numbers by themselves are of little good without the corresponding spectral distribution. Close-in jitter, say <10 Hz, is more detrimental than jitter at 1 kHz. So, as the reflections alter the decision point, they alter the spectral distribution.
I know.....a lot of technical mumbo-jumbo, but that is it in a nutshell.
If the clock and data were sent via separate cables, this sort of problem would not occur. Which is why one-box solutions will always be better.
What Eldartford describes is basically a Time Domain Reflectometer. I hope to have some pictures of different cables soon. (I need to construct a hood for my camera, so that I can photograph the screen. The TDR I use was made in '63. Back before they had a data port on the back to pull out the data in a form you can make a JPEG with.)
(If someone was to hook up some sort of listening doo-hickey to the point in the circuit where the PLL filter is, you will hear a very distorted version of the programme material.)
Any reflections in the data stream manifest themselves into a change in the data-dependent jitter. Not so much in the actual amount, but the frequency distribution. Absolute jitter numbers by themselves are of little good without the corresponding spectral distribution. Close-in jitter, say <10 Hz, is more detrimental than jitter at 1 kHz. So, as the reflections alter the decision point, they alter the spectral distribution.
I know.....a lot of technical mumbo-jumbo, but that is it in a nutshell.
If the clock and data were sent via separate cables, this sort of problem would not occur. Which is why one-box solutions will always be better.
What Eldartford describes is basically a Time Domain Reflectometer. I hope to have some pictures of different cables soon. (I need to construct a hood for my camera, so that I can photograph the screen. The TDR I use was made in '63. Back before they had a data port on the back to pull out the data in a form you can make a JPEG with.)