@brotw, thanks for the mention, and for your comments.
However while I of course agree that spectral components at very high frequencies are present in Ethernet signals when audio data is being conveyed, certainly extending up to hundreds of MHz and probably to a significant degree into the GHz region, I would have to disagree with your analysis.
The factor of 2^16 (or 65,536) in your analysis, which of course corresponds to the number of possible signal levels that can be defined by Redbook data, is not being used correctly. What is being conveyed for each sample (for each channel) is simply 16 bits, not 65,536.
So to be precise, given also that the 8b/10b encoding used by Ethernet increases the number of bits by 25%, your equation should be:
16 bits/sample x 44,100 samples per second x 2 channels x 1.25 = 1.764 MHz
The reason spectral components can be present at hundreds of MHz or more can be analyzed approximately as follows:
My understanding is that both 100 mbps and 1000 mbps Ethernet transmit packets of data at clock rates of 125 MHz, which corresponds to a clock interval of 8 ns (nanoseconds). The risetimes and falltimes of the signal must therefore be significantly less than 8 ns. Let’s say 2 ns. If we assume first order rolloff, risetimes and falltimes of 2 ns correspond to 3 db of rolloff at 0.35/2 ns = 175 MHz. First order rolloff corresponds to 20 db/decade, so the spectral content of those risetimes and falltimes would only be down 20 db at 175 MHz x 10 = 1.75 GHz!
Thanks again. Regards,
--Al