[time-nuts] Re: Phase Noise Measurement in Dallas

[Chris Caudle]

On Wed, October 26, 2022 9:11 pm, Thomas Tammann wrote:
> I use the OCXO on one of my specialized network switches
...
> And yes, there are people out there claiming to measure the difference and
> that these differences have an influence on sound. I guess the causality
> is still hard to prove.

Yeah, the Ethernet clock is not related at all to the audio clock used in
the D/A converter, even for synchronous audio-over-IP designs like Ravenna
and Dante.  Consumer music players (as opposed to professional audio
production equipment) do not even have a synchronized clock, they
free-run.  Zero link between the Ethernet clock in the switch and audio
quality. The quality of the clock to the digital-to-analog converter does
influence quality, but again there is absolutely zero link between the
Ethernet clock and the audio clock.

> Now the maker of this switch claims that an external clock has to have a
> phase noise better than 125dB at 10Hz to make a difference.

According to that link you provided it does have a Crystek crystal
oscillator, which is relatively low noise.
You can see the specs here:
https://www.crystek.com/crystal/spec-sheets/clock/CCHD-575.pdf

> I got likely scamed with my clock from China claiming 140dB @ 10Hz

If it is working well an ovenized SC cut oscillator should be able to
reach that.

> hence, yes I want to measure it ;-) and I really just need to know the
> phase noise (and Allen dev) at the actual output, no any converter. I hope
> that makes all sense.

What you are attempting to do is understandable.  The entire premise
behind it doesn't make sense from a technical standpoint, but the starting
point is relatively straight forward, compare the phase noise spec of your
surplus OCXO to the Crystek spec to make sure your new oscillator is
better than the oscillator internal to the device.

-- 
Chris C