Power supply for ethernet switch?

@amtprod 

My, my. Saying the f word to another forum member. And I am the one who needs to calm down? 

@mclinnguy yea I don't tolerate people coming at me with attitude and talking to me like I said or did something idiotic, like ignorantly ask if an 'audio engineer' is like a "sanitation engineer". 

@amtprod 

I meant no attitude towards you, only questioning the title of "audio engineer" which I assumed was not an actual academic study leading towards an actual degree, and would degrade the title of "professional engineer". 

But it is! I stand corrected: One can obtain a bachelor's and post graduate degrees in audio engineering. 

No idea what Julian has for education; if he is an actual engineer. Of course we all know there are many who make a few recordings at home and all of a sudden they are calling themselves an "audio engineer". 

Hans is a member of the audio engineering society, since 1884, not sure if Julian is. 

https://www.aes.org/aes/hansbeekhuyzen

** Sorry Hans, you are not that old- typo- that should say 1984

@mclinnguy

Well, I’ve re-read the article on Alpha Audio entitled “Hard evidence: a network affects playback quality” and am little the wiser.  Alpha Audio is a Dutch audio blog started by Jaap Veenstra, a journalist with an interest in audio.

Deep in the comments on the article there is a statement that the jitter was measured on the output from the clock feeding the input to the Sabre ESS DAC included in the streamer.

In response to the first comment

“You say that these minor differences in switch jitter are “audible”. How did you determine this? What science is behind this claim?”

moderator Martijn replied

“We use two very special fleshy flaps that are attached to the sides of our heads to determine audible differences. The science part is that we do not claim to do science”.

The issue for me is that this last statement is patently true, but conflicts with the headline “Hard Evidence”, and the way that the results have been used in this topic.

In the past, the Alpha Audio blog has used high-street kit speakers to assess sound quality.

Here’s part of what I think they did.  They took a fairly low-end streamer and “placed it in the RF-shielded measurement box”. Also in the box seems to be other active electronic components of the test measuring system, plus an Ethernet connection, probe cables and an extension lead.  Almost the entire cover (Faraday cage?) of the streamer has been removed.

Anyone familiar with microwave ovens knows that a Faraday cage can keep RFI in as well as out!  Also that wires entering the cage can carry noise.

They used the streamer’s external 5-Volt switching power supply.  The streamer includes a CPU running at more than gigahertz speeds, plus a wireless hot spot.  In other words, the streamer itself is potentially electrically extremely noisy.

They picked three common Ethernet switches and a couple of extra power supplies.  They did not say what speed Ethernet they used, but Gigabit would make sense.

If we exclude airborne RFI (big if) the obvious source of jitter is noise carried on the power supply lines between the switches and the streamer.  Considering the number of switched mode power supplies in the chain, this is hardly surprising.

It is possible that some electrical noise is carried by the Ethernet cable, probably of the unshielded twisted pair type.  A good baseline would have included measurements without the Ethernet cable, and without the switches and their power supplies.  I did not see any such baselines in the results.

Now for the claim that there is a difference of 30 picoseconds of jitter.  Run the DAC on two channels at 192-kHz to get a sample rate of 384-kHz.  That’s about 2.6 million picoseconds per sample.  So 30 picoseconds represents a timing error of about 1 part in 100,000.  That is smaller than the resolution of amplitude on a CD.  I would title the article “No evidence: a network affects playback quality”