CLOCKS, what should we look for in next generation

[jabbr]

50 minutes ago, mansr said:

The Leeson effect has nothing to do with this. I'm talking about a direct mathematical consequence of phase noise in the clock on the reconstructed signal in a D/A converter.

 

Ok, we discussed that in another thread. 

 

Phase noise at 1Hz is an error of 22 MHz +/- 1 Hz and the level of the corresponding frequency variation is this level x f/22 MHz . Phase noise at 10Hz offset is roughly f/2 MHz ...

 

So how much below -120 dB is audible? (That’s roughly the frequency error if the phase noise is 0dB!!! at 10 Hz)

 

The error for >10 Hz for reasonable good clocks is already very low.

[mansr]

Maybe clock phase noise at 1 Hz isn't actually audible despite the widespread rumours to the contrary.

[jabbr]

56 minutes ago, mansr said:

Maybe clock phase noise at 1 Hz isn't actually audible despite the widespread rumours to the contrary.

If you look at the frequency vs phase noise curves there is a flat baseline perhaps -140 - 170 dBc/Hz, as the frequency approaches 0 Hz the phase error rises logarithmically. 

 

So the phase noise > 100Hz shouldn’t be audible, if anything is audible it is the close in noise. 

 

The point is that the effect of phase noise goes down linearly as clock frequency goes up, but the performance of the crystal at close in frequency offsets goes down logarithmically so as sampling goes up with clock frequency there is a net reduction in the effect of phase noise.

[Miska]

28 minutes ago, jabbr said:

The point is that the effect of phase noise goes down linearly as clock frequency goes up, but the performance of the crystal at close in frequency offsets goes down logarithmically so as sampling goes up with clock frequency there is a net reduction in the effect of phase noise.

 

This is why you don't want to have clock dividers! IOW, case where MCLK is higher than the actual modulator output rate!

 

With simple SDM DACs without DSP, one doesn't need MCLK at all. Only data and BCLK (and WCLK in case you do multi-level SDM). And the actual conversion is then run out from BCLK. Which can be something like 24.576 MHz (allowing use of CCHD-957 for example).

 

[Miska]

On 2/12/2019 at 3:44 AM, jabbr said:

The digital FIR but the subsequent analog filter should diminish the 22 MHz +/- component to the point where - 100 dBc/Hz phase error becomes ??? voltage variation ... below any reasonable noise floor ... no?

 

You are now talking about something that is not time-invariant? Or are you still talking about clock line delay for conversion latch?

 

For static delay, you can think about moving some of the unity-weighted FIR taps sub-sample amount in or out. But that amount doesn't change over time, it is the same all the time (because PCB trace length doesn't change). You can model this in digital domain with suitable amount of oversampling if you like. Effect is change in the filter frequency response (if we disregard the other more beneficial effects). So no effect in pass-band, but some effect on transition band.

 

[jabbr]

38 minutes ago, Miska said:

You are now talking about something that is not time-invariant? Or are you still talking about clock line delay for conversion latch?

No here I’m talking about the +/- 1  Hz component which is at -100 dBc/Hz (phase noise level) ie the error signal compared with the center 22 MHz. That error ripple will itself be attenuated by the analog LPF. 

[Miska]

2 minutes ago, jabbr said:

No here I’m talking about the +/- 1  Hz component which is at -100 dBc/Hz (phase noise level) ie the error signal compared with the center 22 MHz. That error ripple will itself be attenuated by the analog LPF. 

 

Noise components are transfered down in the ratio of frequencies as discussed earlier, and the analog LPF cannot fix it. Converting same sample multiple times (through AFIR or similar) helps reducing it though because it affects transformation of the clock to analog domain. The boundary where conversion happens is the critical point where the clock becomes embedded into the analog signal.

 

[Miska]

Ultimately, phase noise defines how well energy of a single discrete frequency in digital domain is concentrated into actual analog frequency component. So this time, instead of talking about time-domain blur, we can talk about frequency domain blur... Of course the two are also related, but often discussed separately.

 

 

[jabbr]

4 minutes ago, Miska said:

Ultimately, phase noise defines how well energy of a single discrete frequency in digital domain is concentrated into actual analog frequency component. So this time, instead of talking about time-domain blur, we can talk about frequency domain blur... Of course the two are also related, but often discussed separately.

 

 

Right, so perhaps my attempt at a time domain analysis isn’t helpful.

 

Frequency domain is easier and 1/22e-6 @  > -100 dBc is a very very small number

[jabbr]

BTW: if anyone wants an excellent OCXO 10 mHz, -120 dBc/Hz @ 10 Hz : these are available by the scores for ~$15-25 on ebay, and you could use this: https://www.tapr.org/~n8ur/PulsePuppy_Manual.pdf for $70 to driver, just add a good power supply and you are good to go for <$100 + power supply

 

So anyone can get this level of performance and no need to spend $500 - $5000

 

(not that its needed or helpful but one wants to experiment ...)

[mansr]

From Stereophile:

JVS: You don't believe in using an external word clock. Why?

EM: Because I think this is the most stupid thing I've ever heard in the audio business. That means you have a precision clock that you have to connect to a wire to connect to a DAC, when the clock should be straight away where it belongs, inside the DAC, beside the DAC chip, if there is such a thing—not through a cable in a different box. This is so idiotic, it's not even funny. It's a money grab.

[barrows]

10 minutes ago, mansr said:

From Stereophile:

JVS: You don't believe in using an external word clock. Why?

EM: Because I think this is the most stupid thing I've ever heard in the audio business. That means you have a precision clock that you have to connect to a wire to connect to a DAC, when the clock should be straight away where it belongs, inside the DAC, beside the DAC chip, if there is such a thing—not through a cable in a different box. This is so idiotic, it's not even funny. It's a money grab.

I suppose that would be Ed Meitner?

[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.) 

[jtwrace]

34 minutes ago, mansr said:

From Stereophile:

JVS: You don't believe in using an external word clock. Why?

EM: Because I think this is the most stupid thing I've ever heard in the audio business. That means you have a precision clock that you have to connect to a wire to connect to a DAC, when the clock should be straight away where it belongs, inside the DAC, beside the DAC chip, if there is such a thing—not through a cable in a different box. This is so idiotic, it's not even funny. It's a money grab.

He's not the only one I've heard say that.  

[mansr]

1 hour ago, barrows said:

I suppose that would be Ed Meitner?

Yes, should've edited the quote to make that clear.

[barrows]

It is always nice to hear when an experienced digital engineer make no nonsense statements like that.

[Emm]

I Imagine how one with external clock, will feel after having read this statement coming from a designer like Ed Meitner

[mansr]

9 hours ago, Emm said:

I Imagine how one with external clock, will feel after having read this statement coming from a designer like Ed Meitner

They'll feel smug, "knowing" that they are better informed even than him.

[plissken]

17 hours ago, mansr said:

From Stereophile:

JVS: You don't believe in using an external word clock. Why?

EM: Because I think this is the most stupid thing I've ever heard in the audio business. That means you have a precision clock that you have to connect to a wire to connect to a DAC, when the clock should be straight away where it belongs, inside the DAC, beside the DAC chip, if there is such a thing—not through a cable in a different box. This is so idiotic, it's not even funny. It's a money grab.

 

Continued:

 

Quote

JVS: I believe one of the arguments for an external clock is that it offers better shielding from power supplies, and will thus operate better.

EM: Yeah, especially with units [that] have a separate power supply. There's a lot of shielding there. The whole thing is funny.

MP: In our DACs, the reference clock is inside the product and an inherent part of the conversion circuitry. Anything that comes from the outside world, on whatever input we select, is buffered and reclocked, so we don't have to worry about the artifacts of an external clock. Everything is reclocked to our internal reference. That's what we mean by asynchronous clock design. **

The rest doesn't matter. The rest is bits.**
 

 

Quote

Read more at https://www.stereophile.com/content/meitner-emm-dv2-dsd-mqa-digital-audio#Wu7VUPZEWVMmB9op.99

 

[Emm]

1 hour ago, mansr said:

They'll feel smug, "knowing" that they are better informed even than him.

 

It happens for him to be the father of SACD and the creator of probably the best (after MSB) DAC

[mansr]

8 minutes ago, Emm said:

It happens for him to be the father of SACD and the creator of probably the best (after MSB) DAC

Doesn't matter. Every audiophile "knows" that every widget he's bought is absolutely essential to lifting those veils. Anyone calling them silly is clearly too tin-eared to hear the "obvious" improvement.

[Emm]

5 minutes ago, mansr said:

Doesn't matter. Every audiophile "knows" that every widget he's bought is absolutely essential to lifting those veils. Anyone calling them silly is clearly too tin-eared to hear the "obvious" improvement.

You are right I will quickly sell my DA2 to get a real dac with external clock and if i will not like it i will upgrade the clock's cables 

[Teresa]

30 minutes ago, mansr said:

Doesn't matter. Every audiophile "knows" that every widget he's bought is absolutely essential to lifting those veils. Anyone calling them silly is clearly too tin-eared to hear the "obvious" improvement.

 

What about audiophiles who return stuff because they don't hear a difference or because it makes their music sound worse? Do they lose their audiophile credentials?

 

BTW if I don't hear a difference, someone else might hear a difference that improves their sound, who am I to judge them? IMHO everyone hears differently, have different listening rooms, different ears and different brains. And that is why I never call anyone silly or tell anyone what they cannot hear.  

 

I'm sure Ed Meitner is correct that external clocks are idiotic and a money grab, he's a famous audio designer and that carries weight. Statements by audiophile don't IMHO.

 

P.S. There are modifiers that will upgrade a clock internally.

[Arpiben]

17 minutes ago, Emm said:

You are right I will quickly sell my DA2 to get a real dac with external clock and if i will not like it i will upgrade the clock's cables 

 

Upgrade DA2 with DV2 for having MQA 😁

Nobody is perfect, including Ed Meitner.

[Emm]

41 minutes ago, Arpiben said:

 

Upgrade DA2 with DV2 for having MQA 😁

Nobody is perfect, including Ed Meitner.

i really don’t care about MQA and Tidal, i have quit the service. Only Qobuz for me