Cybershaft rubidium clock...low priced option?

[JohnSwenson]

BTW, instead of the OCXO Limited, would the "double clock mounted" be a good step up from the Premium?

 

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A rubidium standard offers NO advantage over the very good OCXO. The rubidium standard has two systems, a rubidium oscillator, which has high jitter but very good long term stability and an OCXO with very low jitter but not as good long term stability. Some complex circuitry in side there reads both and every so often slowly tweaks the OCXO to match the long term averaged frequency of the rubidium oscillator.

 

Because the OCXO is an adjustable oscillator it actually has slightly higher jitter than the fixed OCXO. Audio could care less about absolute frequency accuracy over tens of years time frame so the rubidium version has higher jitter and costs more, not particularly a good combination for audio use. (unless it is all about bragging rights, but that is something else!)

 

The phase noise specs for those cybershaft OCXOs are actually very good for the price. The big issue with any such external frequency reference is how it gets into the DAC and what happens to it in there.

 

First off, many frequency standards are sine wave output, a lot of DACs that have external inputs want a square wave not a sine wave. Make SURE the reference and the DAC will work together before spending any money.

 

Almost no DAC or audio device uses 10MHz directly. In order to use it the frequency has to be converted. What that conversion does to the phase noise of the input can vary wildly. The absolute best systems out there are at about on par with the phase noise from the premium. So with a premium you would be getting about twice the jitter inside the DAC. With the limited the internal jitter is going to be several times higher than the reference, hence there is not going to be much of an actual difference in the DAC, for a much bigger cost.

 

The above assumes your DAC has a state of the art frequency conversion circuit, these are pretty rare and expensive but COULD exist in one or two audio devices. The problem is that any device with such a conversion circuit probably already has a REALLY good local oscillator, so using one of these OCXOs going through the conversion is not necessarily going to give you lower jitter in the DAC. It may, but it may not.

 

John S.

[JohnSwenson]

I just could not believe a 20K USD clock couldn't do the best job. If 1000USD clock can improve SQ of 20K dCS clock, this means dCS did really bad in clocking regards that price tag.

 

 

Sent from my iPhone using Computer Audiophile

 

Not really, if you are coming from a pro audio perspective where everybody feeds things with external clocks, you just assume everyone is using a really good external clock and the internal clock is just an emergency backup if somehow the external clock breaks. In other words, if you know everyone is using an external clock, why bother with a really good internal clock?

 

That doesn't mean an external clock is the BEST way to go for home audio, just that the dictates of pro audio do it that way.

 

John S.

[JohnSwenson]

Fair point on the comparison.

 

There is nevertheless a valid debate to be had on whether one XO type is 'better' than another for DAC usage based simply on a comparison of the published specs. The jitter ranges I have provided links to show (or at least attempt to show) a better context for audio DAC usage. My own listening tests have led me to conclude that following the published specs will not always give you better sound - there are other factors at play.

 

To conclude, I would not have believed that an XO (and possibly its location) could have such an influence on sound these days. My hearing is not the best, and I am usually pretty cynical when it comes to real vs perceived differences, but I have found that swapping the XO influences a DAC's sound perhaps more than any other component change I have tried.

 

The DAC does have to do something reasonable with the clock signal. I have seen many DACs that spend a lot of money on high performance oscillators, then do really stupid things with the signal, completely ruining any advantage that high performance oscillator could have provided.

 

I had an interesting experience with upgrading clocks years ago. I had built my own DAC with an I2S reclocking circuit fed from a low jitter oscillator. I got the I2S from a hacked up squeezebox, and fed the clock from the DAC back to the SB to sync it to the DAC. The signal integrity between the boxes was atrocious, but it didn't matter because the signal was reclocked

 

One day I decided to listen to the audio out of the squeezebox, WOW it sounded so much better, not as good as my homebuilt DAC, but WAY better than the original without the external clock, even though the clock from the DAC was highly distorted by the really bad digital interconnect I used. I expected it to sound worse given the SI of the clock I was feeding it, but the low jitterness of that clock managed to make it through.

 

John S.