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Old 9th November 2014, 09:28 PM   #491
acko is offline acko  Australia
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Originally Posted by soekris View Post
The DAC design itself is not bound to clock frequencies, but in master mode I'm expecting to support 45/49 from the Si514, that will enable up to 3 Msps. But the Si514 version I'm using can go up to 125 Mhz, so I do have the options to go 90/98 if needed, either for 6 Msps or for higher speed digital filters. But I like to keep clock speed down.
Thanks again!
I reckon 45/49 is good enough for the time being.
Next question, if you do not mind , can your DAC be 'Slaved' to an external clock instead say from a transport clock or external Clock module with CKSEL coming from the external source?
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Old 9th November 2014, 09:41 PM   #492
soekris is offline soekris  Denmark
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Thanks again!
I reckon 45/49 is good enough for the time being.
Next question, if you do not mind , can your DAC be 'Slaved' to an external clock instead say from a transport clock with CKSEL coming from the external source?
I'm not sure what you mean.... The DAC have like a optimized digital PLL, it simply continuously measure the clock, then decide if the internal clock need to be corrected, with the FIFO takes up any slack. And the internal clock is probably better than any external clock over long wires.

So in slave mode it will in principle lock to anything you feed it, don't even need a CKSEL to help. Since you always have a bit clock, either from SPDIF or from I2S, it don't need anything else.
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Old 9th November 2014, 10:11 PM   #493
esgigt is offline esgigt  Netherlands
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Quote:
Originally Posted by soekris View Post
I'm not sure what you mean.... The DAC have like a optimized digital PLL, it simply continuously measure the clock, then decide if the internal clock need to be corrected, with the FIFO takes up any slack. And the internal clock is probably better than any external clock over long wires.

So in slave mode it will in principle lock to anything you feed it, don't even need a CKSEL to help. Since you always have a bit clock, either from SPDIF or from I2S, it don't need anything else.
Søren,

if I understand you correctly, within certain limits the Si514 controlled clock stays constant while the "clock" of the input signal deviates. Could you please explain under which conditions the Si514 controlled clock will change? Or does the answer go too deep, technically speaking? (just trying to understand how it works... )

Thanks in advance,
Edwin
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Old 9th November 2014, 10:14 PM   #494
acko is offline acko  Australia
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Quote:
Originally Posted by soekris View Post
I'm not sure what you mean.... The DAC have like a optimized digital PLL, it simply continuously measure the clock, then decide if the internal clock need to be corrected, with the FIFO takes up any slack. And the internal clock is probably better than any external clock over long wires.

So in slave mode it will in principle lock to anything you feed it, don't even need a CKSEL to help. Since you always have a bit clock, either from SPDIF or from I2S, it don't need anything else.
Thanks Søren, you have clarified well enough.
I was actually referring to the possibility of an external master clock option to replace the Si514 on your DAC. e.g. using this new Pulsar Clock or similar to improve on the overall jitter performance
I guess the internal operation of your DAC does not allow this mode?
Regardless of clocks, this is an excellent design and the potential to use with external digital filters makes this a standout product. Well done
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Old 9th November 2014, 10:41 PM   #495
soekris is offline soekris  Denmark
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Originally Posted by esgigt View Post
Søren,

if I understand you correctly, within certain limits the Si514 controlled clock stays constant while the "clock" of the input signal deviates. Could you please explain under which conditions the Si514 controlled clock will change? Or does the answer go too deep, technically speaking? (just trying to understand how it works... )

Thanks in advance,
Edwin
It goes something like this:

When not locked, the DAC's FPGA/uC will measure the input clock at very short intervals, until something in a standard sample rate show up.

It will then measure the clock over a little longer time, using that result to program the clock oscillator.

Set FIFO at half full, then open up for audio output.

It will continued to measure input clock over longer time, using that to make small adjustments as needed, the Si514 can be adjusted +-1000 ppm glitchless.

If clock goes out of large range for short period, or smaller range over longer time, the audio will be muted and DAC declared not locked.

FIFO will take up any slack insuring no jitter. If input clock is long term stable then adjustments will be very few and very small.

Repeat.
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Old 9th November 2014, 10:51 PM   #496
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From what i can see is in the datasheet the

Si514 is capable off :

100Hz –86dBc/Hz
1 kHz –108dBc/Hz
10 kHz –115dBc/Hz

@156MHz

A common CCHD957 @ 49MHz

100Hz –129dBc/Hz
1 kHz –153dBc/Hz
10 kHz –161dBc/Hz

Assuming the the Phase noise is constant regardless of output frequency should give the Si514 some -9dbc/Hz better numbers at 49Mhz but it still much much noisier.
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Old 9th November 2014, 10:55 PM   #497
acko is offline acko  Australia
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Quote:
Originally Posted by soekris View Post
It goes something like this:

......

It will then measure the clock over a little longer time, using that result to program the clock oscillator.

...
It will continued to measure input clock over longer time, using that to make small adjustments as needed, the Si514 can be adjusted +-1000 ppm glitchless.
What is the nominal clock frequency?
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Old 9th November 2014, 11:08 PM   #498
acko is offline acko  Australia
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Assuming the the Phase noise is constant regardless of output frequency should give the Si514 some -9dbc/Hz better numbers at 49Mhz but it still much much noisier.
Agree, from what I can see the absolute jitter performance depends on the on-board Si514 Clock and will limited by this. Any option to handle a premium external clock will take this DAC to greater heights. From my experience, piping in external clocks over short lengths of coax (50mm) has no detrimental effects. If fact keeping clock generators off the DAC board isolates switching noises from sensitive analog sections
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Old 9th November 2014, 11:34 PM   #499
soekris is offline soekris  Denmark
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Quote:
Originally Posted by Tazzz View Post
From what i can see is in the datasheet the

Si514 is capable off :

100Hz –86dBc/Hz
1 kHz –108dBc/Hz
10 kHz –115dBc/Hz

@156MHz

A common CCHD957 @ 49MHz

100Hz –129dBc/Hz
1 kHz –153dBc/Hz
10 kHz –161dBc/Hz

Assuming the the Phase noise is constant regardless of output frequency should give the Si514 some -9dbc/Hz better numbers at 49Mhz but it still much much noisier.
I don't look that much at the phase noise spec, but instead at the jitter specs. Here the Si514 have max 1 pS RMS, while the best SPDIF receivers have 50 pS RMS, and many people seems to be happy driving a DAC chip directly from a SPDIF Receiver.

The big question is: What can you hear ? I have searched the web and found references to a number of studies, they varied a lot, with hearable limits of 20 pS to 250 nS, with the most credible ones with hearable limits in the nS range.... So I consider 1 pS RMS jitter to be perfectly fine. Especially as once the clock goes though the digital logic it is not 1 pS anymore....
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Old 9th November 2014, 11:43 PM   #500
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Quote:
Originally Posted by soekris View Post
The big question is: What can you hear ? I have searched the web and found references to a number of studies, they varied a lot, with hearable limits of 20 pS to 250 nS, with the most credible ones with hearable limits in the nS range.... So I consider 1 pS RMS jitter to be perfectly fine. Especially as once the clock goes though the digital logic it is not 1 pS anymore....
What you can hear depends on the DAC chip being used - S-D or multibit. For multibit the jitter tolerance is quite a lot higher - 1pS sounds to me like considerable overkill Those using S-D converters have their work cut out though getting low enough jitter since the OOB HF output folds-down into the audio band as noise when jittered.
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