Superclocks

[mmerrill99]

28 minutes ago, jabbr said:

Here's a spec sheet on a widely available part that goes for $14: http://www.crystek.com/crystal/spec-sheets/clock/CCHD-575.pdf

 

You'd want the close-in phase error (e.g. @1Hz) to be substantially better than this -- note that this is "femtosecond" range, so be very very careful before spending $$$ on marketing fluff.

Some other points: about the measurements shown on clock datasheets:

- is this a random clock from a batch that was measured or is it the'best' one found during manufacturing? In other words what's the quality range of these clocks - 10%, 20%, 50% tolerance?

- What PS was used for the measurement - was it a standard PS found in most audio devices or some high quality laboratory supply?

- What other conditions applied when taking these measurements - ensuring constant temperature, faraday cage, etc?  

[mmerrill99]

6 minutes ago, Superdad said:

 

Reasonable points and questions: Yes, the oscillator manufacturers are measuring their clocks--and the performance of those is of course not at all the same as the jitter performance of a complete DAC.

 

I will tell one interesting story:

Crystek has gotten a LOT better making their XOs!  18 months ago John and I requested and received samples of their CCHD-575 (the one Jonathan linked to above).  Got 25.0MHz version (for testing in the ISO REGEN).  They sent us 3 samples, and they each came with individual phase-noise plots.

Whereas the data sheet on Crytek's web page shows -100dB for 10Hz offset (in the mid-20MHz f-range we are using), the plots for the 3 samples we got were -108dB, -110dB, and -112dB at 10Hz!   

Of course our first thought was that they hand-selected these and that production runs could not be anywhere near as good as these.  So I immediately picked up the phone and called Crystek (they are actually not that large a company; one sales engineer seems to handle the whole country).  They said no, the samples were not at all specially selected--just measured right off the line. And he said that their processes have improved so much that the $9.60 CCHD-575 (that's what I paid for the first 500 pieces; goes to $9.30 ea. @ 1,000) now outperforms their big $27 CCHD-957 as used in a lot of top-tier DACs.   I told him they ought to update the 575's datasheet on the web to reflect that.  Guess he did not relay that suggestion to their marketing department. 

 

Of course if you want to see eye-popping phase-noise performance, then check out the Pulsar Clock. -118dB to -123dB at 10Hz!  But it is 420 Euros...

That's a good start - I didn't know they sent out phase noise plots with their clocks.

 

Did you get 500 plots then or is it just samples that plots come with?

 

Maybe they didn't update their datasheet because ......... - call me a cynic, hell call me anything you like

[mmerrill99]

54 minutes ago, ElviaCaprice said:

Sorry, I fail to see the relevance to the subject on hand.  This article fails to even mention the DAVE's clocking.  The real question is why does, what appears to be, great additional clocking outside the DAC make a big difference in SQ with the DAVE?

Well Uptone/Swenson's reasoning for better clocks (& therefore better signal integrity, lower jitter) was that it required less overhead at the chip receiving & processing the signal. The logic was that this reduction in overhead generated less internal noise on the ground plane of the chip & ultimately on the ground plane of the power distribution system to which the sensitive DAC chips are connected & effected by such small noise fluctuations.

 

Unfortunately, it appears that these noise fluctuations are very low in amplitude & difficult to measure.

 

Now how a clock on a purely digital upstream device can audibly affect the DAC requires a deeper system analysis  

[mmerrill99]

1 hour ago, STC said:

 

It is possible that clock can affect the SQ. This article answers all those questions raise here

 

http://www.soundonsound.com/techniques/does-your-studio-need-digital-master-clock

 

Conclusions

Overall, it should be clear from these tests that employing an external master clock cannot and will not improve the sound quality of a digital audio system. It might change it, and subjectively that change might be preferred, but it won't change things for the better in any technical sense. A‑D conversion performance will not improve: the best that can be hoped for is that the A‑D conversion won't become significantly degraded. In most cases, the technical performance will actually become worse, albeit only marginally so.

Pretty dubious conclusions based on limited tests - way over generalised from the specific.

 

I wouldn't for a minute claim that  "This article answers all those questions raise here"