Superclocks

[Superdad]

40 minutes ago, mmerrill99 said:

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?  

 

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...

[Superdad]

1 hour ago, jabbr said:

 

Then there is building your your own ala the @andrea_mori thread on DIY. Having a good crystal is particularly important as is a clean power supply. Crystals from Laptech in Canada. One point to remember is that the specs get worse as the oscillator frequency goes up (physics) so best to use the lowest frequency you need. This suggests that for DSD, perhaps DSD1024 won't be better than DSD512 but the exact point when things get worse is as yet unknown. For USB and Ethernet it is entirely unclear that doing any better than a Crystek will give any better performance. Measurements to demonstrate this are sorely lacking.

 

You are of course correct on all counts there.  Though John and I followed Andrea Mori'sclock thread for a while--they certainly when to a lot of interesting lengths--it seems that in the end the exercise resulted in clock boards which still just had comparable phase-noise, nothing eye-popping that I can recall, though it has been a while since I checked in on that project.

 

As for USB and Ethernet clocks, yeah, we don't see any need to go crazy on those.  But early on in the ISO REGEN dev cycle we had boards populated identically except that one set had just the CCHD-3391 as used on all original USB REGENs since the beginning, and the other set had the CCHD-575.  In auditioning the two, it took all of 15 seconds for us to decide that $8.40 per board ($1.20 versus $9.60) was WAY more than worth it.  VERY AUDIBLE!  Though I admit that for a USB clock it almost does not make sense that it would be so audible. 

[Superdad]

13 hours ago, 2string1 said:

Next it will be, SUPER DUPER CLOCK!!!

 

Not as good as SUPER ULTRA FEMTO clocks--with rubidium cufflinks for good measure...

 

Phase-noise: it's what toddlers do to get their way until they learn how to shout "NO!"  

[Superdad]

3 hours ago, barrows said:

You have measured differences within the range which would be audible?  That is <20kHz and above -110 dB?  Really?  I mean, I get that an early rolloff filter could be considered a measurable/audible difference (although not theoretically for my hearing)-but what about minimum phase vs. linear, for example...

 

4 hours ago, Miska said:

It is not something that would elude measurements but be audible subjectively. Sometimes the differences are easier to analyze than to hear.

 

Ah, the crux of the biscuit as Mr. Zappa would say!  

 

a) Many of the "objectivists" say that if you can't measure the differences as THD, IMD, or frequency response in the 20-20KHz band then you can't hear it; Thus they claim that all these variations in filters must be inaudible and that we are delusional.

 

b) Anyone who has either designed or played with digital filter parameters will tell you that the differences of steepness, cutoff, length, and phase are readily audible;

 

c) Yet Jussi and DAC designers will mostly look at their filters' ultrasonic FR and impulse response.

 

So who is all wet in this?  

 

[Superdad]

2 hours ago, barrows said:

Of course a lot of those same people also claim to be able to "see" the invisible aliens walking among us...

 

Don’t you?  There must be at least three taking up residence here on the CA forums.  These aliens know who they are... 

[Superdad]

2 hours ago, barrows said:

OK, I get that the measurements you use to develop filters are the necessary and applicable ones too show that the filter design is doing what you want from a technical perspective, and I have no doubt that many of your filters do sound better/different.  I do not have HQPlayer (yet, unfortunately) because I do not have a good machine to run it on.  But I have tried quite a few different approaches, and the differences are usually small, but meaningful in an audiophile sense.

 

Hi Barrows:

I strongly encourage you to try HQ Player and spend some time listening to a wide range of its filter, dither, and modulator options.  

About 3 years ago I spent months with Audirvan+, fine tuning (by ear with an exceptional NOS PCM1704 DAC) a filter with the 5 iZotope Advanced parameter sliders, down to a fine degree.  And while A+ seems to do a better job bypassing OS X Core Audio (comparison made by using both players w/o any SRC), @Miska's poly-sinc family of filters blew right past the best of what I was able to accomplish.

 

For PCM SRC you really don't need much computing horsepower, and even DSD256 is not terribly taxing.  And of course HQP NAA on a Rendu is perfectly matched.

 

Have a great weekend.  Weather is lovely here so I'm heading out on a bike ride now.  Got to huff and puff a bunch for the good of my sedentary heart and ass.