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In Reply to: RE: Buffering posted by Scrith on September 8, 2011 at 12:24:29:
Thank you for your honesty.
It now appears from Gordon's description of his optically isolated test setup that the effects he was observing did not come from emi/rfi coupled through the air or the transport DAC connection. Assuming that it's not the power wiring (something that could be tested by running the computer entirely off of batteries if that wasn't already done) one is left with variations in the waveforms traversing his optical USB extender.
The significance of an eye pattern is that it shows the presence of information on the cable in addition to the 0's and 1's that are the reason for existence of a "digital" communications channel. These demonstrate that physical reality is not just 0's and 1's due to various forms of signal degradation, viz. rise time, droop, jitter, noise, ringing, and what not. Eye patterns are the living proof that all signals inside computers, and especially on longer signal runs between computers, are not 0's and 1's, but are much more complicated. Unfortunately, human hearing has a dynamic range beyond 100 dB and looking on scope traces one can see noise and distortion no more than 60 dB down (0.1%) and in most cases no more than 40 dB down (1%). So the interesting activity from an audio perspective is hard to see on a scope trace. Specialized (read expensive) equipment is required to go beyond this level. But putting a scope on just about any signal involved with a computer is all that it takes to prove decisively that "bits ain't just bits". This is all well known to computer hardware designers, who are trying to make the signals better so they can run the machine faster or trying to make the signals worse so they can built the machine cheaper so long as it is still sufficiently reliable that they can keep their job. (I worked as an engineer for a large computer company for over 25 years.)
All of this is why buffering is not the whole story, since the buffers are supposedly dealing with bits whereas in reality they are dealing with analog signals, as can be seen by looking at eye patterns.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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Follow Ups
- EMI/RFI, eye patterns, and buffering - Tony Lauck 13:05:34 09/08/11 (3)
- RE: EMI/RFI, eye patterns, and buffering - cfmsp 12:52:57 09/09/11 (2)
- RE: EMI/RFI, eye patterns, and buffering - Tony Lauck 13:17:44 09/09/11 (1)
- RE: EMI/RFI, eye patterns, and buffering - cfmsp 14:59:29 09/09/11 (0)
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