CLOCKS, what should we look for in next generation

[Superdad]

15 hours ago, beerandmusic said:

Is it possible that if we didnt have a usb interface, e.g. network to dac in one box, that we could just have one clock?

 

Other that the exception I will mention, one clock will never be the case.  

Every processing chip (and even some chips that we don't think of as processors) needs a clock source.  So for the interfaces it does not matter if it is an Ethernet switch or PHY, a USB hub or PHY, the processors or FPGA associated with them, they all need a clock source.  As does any general purpose processor, be it a ARM or Intel type, or graphics or DSP.  

Such clocks will most always be at whole number frequencies, 12MHz, 13MHz, 24MHz, 25MHz being the most common.

 

Audio rate clocks as part of a DAC will never match those: they will typically (with exceptions for ASRC or very high sample rate conversions) be multiples of 22.5792MHz and and 24.576MHz.  

And there really is not much good reason to source together the various chip clocks and the audio bit clocks since most designs are already doing their best to keep these circuits isolated from one another.

 

There is one method that can be effective if done right: And it is a category which John well and will likely post about as he has time.  Those are clock synthesizers, the most modern of which can even go a ways to attenuate jitter.  Generally these chips get pair with a really good, low phase-noise reference clock (XO or OCXO) of any selected frequency.

BTW, the SOtM clock boards use a clock synthesizer chip (and a reference of unknown caliber) to generate the multiple selectable frequencies you see offered on their web site.

 

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Separately, I will state that we think what is needed to advance is a wholly different interface between computer and DAC/DDC.  One that truly is immune to all upstream vagaries and cables.  But one that does not require anything in the form of processor, OS, or driver s/w in the DAC--and which can run over long lengths of wire with no degradation.

It may take another year for this to come out--and we do not hold any illusions about instant acceptance/adoption, but this is one of the things that John and I have been working towards for a long time.  I will not say anything more about it, so don't ask.  Suffice it to say that the status quo, with regards to computer>DAC interfaces, may not stay the same forever. 

 

[Superdad]

11 minutes ago, beerandmusic said:

re-reading, ok, you are suggesting ethernet based fiber approach, and still need for processor, but as a separate device...those already exist, but would be over the budget I am in. 

 

That s NOT AT ALL what we are working on.  Don't even bother trying to guess.

[Superdad]

17 minutes ago, jabbr said:

For analog circuits including PSU: http://www.analog.com/en/analog-dialogue/articles/understanding-and-eliminating-1-f-noise.html

 

That's a very good article Jonathan, thanks!  (What makes it "good" is that I actually understood most of it. )

[Superdad]

37 minutes ago, Ralf11 said:

Now where have I heard that before!!

 

Probably lots of places since it is widely known that phase-noise/jitter at very low offset frequencies is the most important aspect of clocking performance with regards to audio.  The 100Hz, 10Hz, 1Hz (and even below though rarely published) figures are what audio engineers pay attention to when considering oscillators.

 

Or maybe your question was just rhetorical and snarky. I did not see a question mark...

[Superdad]

3 minutes ago, Ralf11 said:

this describes your comment - what is the problem?

 

Truth is Ralf, I never know what your point is since 90% of your posts are single-line fragments which are often neither questions or statements.  I guess you are just trying to be provocative.  

[Superdad]

48 minutes ago, barrows said:

For a project awhile back, Sonore got a small batch of hand selected NDK oscillators-the few customers who received these got a very special upgrade indeed!  Unfortunately I do not believe the source who made those selections is offering the service anymore.

 

I assume you mean Patrick in Texas.  Have not spoken to him in at least a year.  He can be a bit ornery.  

Last we spoke I suggested he go ahead an measure some Crystek CCHD-575 to verify for himself my claim that they provided us with 3 random production samples of 25.0MHz with paper plots showing 10Hz performance of -108, -110, -112 dBc/Hz--which is vastly better than what Crystek's own published plots show.  Luiz says that their engineer is very conservative and does not want to boast about 575 performance.  I always tell him that his competitors are not shy about doing so.  I wish that John could find those original printouts that came with the samples, but am afraid they got lost in his house move.

[Superdad]

BTW, here's the plot for an eye-poppingly great OCXO we have been looking at.  Have no idea the cost yet--likely $600 a piece.  But check it out: -110dBc/Hz at 1Hz, -143 at 10Hz!  (this is 10MHz part, but even in the mid-twenties audio clock range these are spectacular).

 

[Superdad]

13 minutes ago, PeterSt said:

Also it may not be a good idea to take synthesis for granted now (it really is not for the better as far as I can tell).

 

Not taking them for granted, but the better synths do not add much phase noise at all.  While for a DAC it’s best to go with native clocks, there are times when one needs several frequencies.  An example is our upcoming EtherREGEN, where we need both 25MHz (in several locations) and 250MHz, and we have two completely separate domains.  So two synths and two Crystek 575s fill the bill.

[Superdad]

23 minutes ago, barrows said:

I suppose that would be Ed Meitner?

 

Could be Eddie Murphy.  Or Elon Musk.  Or hey, I know, Eddie Money! (Time is running out for all of them and they could each use a word clock.)