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In Reply to: This is a circular argument that gets nowhere posted by fmak on January 13, 2015 at 05:08:27:
I would call it "mysterious", not "illogical". And mysterious only to the ignorant.
First of all, looking at the signal on the Ethernet cable, there is at best a very loose "temporal nature" of the signal. For the majority of the time while the audio is playing out the speakers there will be no signal on the Ethernet whatsoever. The tolerances involved will depend on the Ethernet protocols used, in some cases one can pull the Ethernet cable and several seconds of audio will continue to play out the speakers.
An Ethernet signal is decoded as a packet. If the data has been changed in any way the packet will be dropped, no data will be decoded. In addition with most implementations of Ethernet receivers the fact of the data corruption will be counted. (And as I showed, it would be extremely rare for there to be any errors in data decoding if the Ethernet components are within specifications.)
What is changing is the content of the noise that is carried on the cable, as well as the timing of the packet itself due to "packet jitter". If the DAC is operating asynchronously, the data will be reclocked with a local clock at the DAC so the timing of the analog audio stream will not be directly affected by the packet jitter. However, there is a secondary effect, namely upon the end of packet reception there is processing involved by the Ethernet receiver (typically by software). This processing uses energy and can be seen by putting a scope on the power and ground lines involved. As John Swenson has shown this power supply noise can couple into the DAC circuitry, specifically the clock and clock circuitry, the converters, the I/V buffer and the output buffer. This noise creates phase modulation of the analog audio stream (jitter) and amplitude modulation of the analaog audio stream, as well as added noise even when the music is silent.
To understand how this can happen it is necessary to understand the operation of all the circuits, in detail, including the properties of the wiring (e.g. power and ground). Because packet systems have buffers, there is a complex relationship between the temporal nature of the signal that varies according to the physical place where the signal is being measured and in the case of software the specific portion(s) of the packet processing code that are being executed.
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
- RE: This is a circular argument that gets nowhere - Tony Lauck 01/13/1508:39:37 01/13/15 (2)
- it is necessary to understand the operation of all the circuits - fmak 18:40:33 01/13/15 (1)
- RE: it is necessary to understand the operation of all the circuits - AbeCollins 08:27:42 01/15/15 (0)
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