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RE: Jitter Measurements

> What you'll see is how the jitter measurement (Jpp) differs significantly.
> The only change in the entire equation is software with all else the
> same (i.e. hardware, audio chain and mains supply). The important thing
> here is that all software matters across all levels
> (firmware/BIOS, operating system, drivers, audio player etc.).

Well, important thing...... the above is simply incorrect statement. As long as software is any good, it doesn’t change a squat about jitter. I didn’t say it is not possible to produce such artifacts by software, I said that one has to screw up something to do that, and this apparently was the case. Everything you have posted was the case where your software screwed something up in this regard. Yet you claim that “all software matters across all levels”.

As for the plots you’ve posted... they generally look too good to be true for PCI based S/PDIF source, and this particular source is most probably driven by PLL clock and with performance claimed by manufacturer “< 1 ns”. Having a PCI S/PDIF source with shown performance would be much more important news than anything else we are now talking about. So, my question is what the PLL corner frequency of Scarlatti DAC is?

Also, for the record... when making the jitter measurements of analog output, it is important to use the frequency that is a divisor of sampling frequency, since only this way you avoid quantization noise, and only that way you comply with proposed standard. Your FFT windowing was also apparently inappropriate. Or, if it was, what was the cause of the skirt around 7kHz?


> That's a bad assumption.

No, it is not assumption at all, it is rather a matter of fact. One has to learn to tell one from the other though. In that regard, the protocols, data processing and alike belong the digital, whereas voltage, current and alike belong the analog world. Connection between these two worlds is possible by so called sampling and that’s where the jitter we are talking about belongs. Anyhow, the “digital is analog”... no way.


> If you don't mind, post one of the 2 plots. Also, the level of optimizations applied on the computer transport you measured.

I actually posted plenty of plots showing performance of PC based audio systems during a couple of last years to the diyhifi.org, and recently you may find a sort of summary on my own site. I am not familiar with the term “the level of optimizations” though.

Pedja


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