I suggest reading Dunn's Tech Note on measuring jitter.
The J-test It isn't a "test" as such, it is a test signal, designed as a "worst case" waveform that makes the jitter as conspicuous as possible. You use it with a FFT analyzer, and a FFT analysis done with a 24-bit soundcard with a decent SNR is more than sensitive enough. Your fancy Microsemi 5125 won't have any more precision that that - the difference is that the Microsemi is designed to measure radio frequencies (hundreds of MHz). That doesn't matter if you measure the DAC output.
At a certain point, everything looks the same with the Jtest. It doesn't take much nowadays to accomplish a perfect Jtest measurement. Measuring the phase noise in the digital domain with a far more precise machine, tells you much more. Today's best DAC clock jitter is in the Femtoseconds. Not in the Nanoseconds like it was back in the 90's.
What level of jitter is audible in your opinion?
I can easily hear the difference swapping clocks with 5dBc phase noise @ 10hz spread. The sound keeps on getting better and better the lower the phase noise gets. I haven't found a limit yet.
Here's the clock that Grimm uses in the LS-1. Obviously they figure phase noise at this level is important as well. Perhaps you should pay old Herbert a visit as he's local to you.
https://www.by-rutgers.nl/rutgerS-Clock.html
5dBc, or 5dBc/Hz? Phase noise is usually measured in dBc/Hz. A positive value of dBc means noise is stronger than the actual signal...
I think I have met him at one of the Dutch VERON (amateur radio association) events. He's into older audio/radio gear, right?
Yes dBc/hz.
Here's his full website. Loaded with all kinds of good information. He probably one of the worlds most knowledgeable experts on audio clocks.
https://www.by-rutgers.nl
I of checked it when you provided the original link. He doesn't say if it was published anywhere.
It's published on his website. That's the only place it needs published. DAC manufacturers who listen to what he has to say discover very quickly that they have great sounding products. So do their clients.
Well I guess that must make the folks at Grimm and Mola Mola fools along with me then. Because we both believe what he has to say.
In audio, peer reviewed publications are only for manufacturers who have no confidence in their abilities to hear. No different than a chef who can't cook a meal without following a recipe book step by step.
So according to you, all peer reviewed publications are just recipe books?
I assume you have never had anything published by something like the AES?
Peer reviews exist to maintain standards of quality and provide credibility. Something self-published on a web-site could be brilliant - or total baloney.
You keep quoting Mola Mola DAC as an example of DSD DAC technology. Perhaps you might like to share a comparison between their measurements and yours ??
https://www.mola-mola.nl/Blog.html
An externally hosted image should be here but it was not working when we last tested it.
I already said it has a dynamic range of 121dB. The Mola Mola gets that dynamic range because they upsample all the way to 100Mhz, and parallel several logic gates together for the DAC section. We upsample to 22.579Mhz. The downside of upsampling all the way to 100Mhz is a 100Mhz clock has far higher phase noise than a 22.579Mhz clock of the same grade. Also even if you could hear a noise floor lower than 121dB, all the components in your playback chain better match as well. Because your noise floor can only as low as the noisiest component in the system. But there's also the element of marketing involved as well. Most people are impressed with bigger numbers. So the decision to upsample to 100Mhz may have had something to do with that.
This is where testing yourself comes into play. Any competent designer has the ability to make their own judgement if something is valid or not after doing their own in house testing.