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In Reply to: RE: " Directstream is super sensitive to input jitter, adding a regen will most likely help." posted by beppe61 on May 27, 2015 at 06:09:58
Hi,
> And this suggests me that this need depends on the specific case.
This tends to my point in all these exchanges. There are a few ways to do things right and many to do it wrong.
> I think that in the end the advantage of USB over spdif justify
> some efforts in its set-up.
Funny you mention SPDIF.
In all the years I also figured out how to do the same thing for SPDIF. The following is the spectrum (24 Bit J-Test) of a SPDIF signal with 50,000pS of 200Hz square-wave jitter deliberately added (the AP2 has such a function).
The upper trace is this SPDIF signal decoded using a "standard" SPDIF receiver (in case you ever wondered what 50,000ps of 200Hz square-wave jitter do to an Audio Signal).
The lower trace is the same signal, but here the clock system that I designed a while back for a very high end DAC is used instead, as we can see, another "perfect" result.
So, again, what matters most is how things are designed. If we understand the problems and requirements - then with sufficient diligence we will find and implement solutions that solve the problems and fulfil the requirements, even with systems that are by design sub-optimal for the given job.
And guess what, this kind of USB and SPDIF performance is standard for any of the digital products I have a hand in, from the cheapest sub 200 USD USB DAC all the way to the "Ultra High End" Tube output DAC...
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Follow Ups:
Very interesting again Mr. Thorsten. Thanks a lot.
With reference to the graph if i understand well in the top trace the clock is set by the source, while in the bottom trace the clock is the one of the receiving dac ?
Very interesting because it shows that reclocking when done right can have spectacular results in terms of jitter reduction.
Very impressive performance indeed.
However i think i have understood the basics. More or less ... but the all issue is extremely complex.
Just a last curiosity ... in the case of the top trace this high jitter is heard during the listening ? which the main effects on sound ?
less focus ? more distortion ?
Thanks a lot again for the very kind and precious advice.
Kind regards,
bg
Edits: 05/27/15
Hi,
Yes, the upper trace is the standard SPDIF receiver PLL with around 20kHz bandwidth, any jitter below 20kHz rides through, only above 20kHz is there any appreciable attenuation.
The lower trace uses a local clock, correct, but without resorting to Sample Rate conversion etc., the principle is actually quite similar to the NAIM DAC clock, the main difference, where the NAIM DAC has 10 total selectable frequencies, our system literally has billions of them, with a single minimum clock step measured in ppb (parts per billion).
As to "is this kind of jitter audible", given that it creates a massive rise in noisefloor and around an effective dynamic range of worse than K7 tape without Dolby, I would expect so. I never listed to this and I cannot use the AP2 to impose this kind of jitter on external (music) signals.
This might an interresting field of research, but I am swamped as is...
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Hi and great performance indeed.
It is impressive the difference between what gets in and what gets out.
I did not think it were possible. I have always been quite skeptical of jitter reducing circuits, like after the damage to the signal is done there is no way to repair.
But then this could be also possible for usb transmission i guess.
And also quite easily measured. A test signal with a lot of jitter and see what comes out.
Very interesting indeed. Thanks again for the very clear graphs.
They explain very well what is going on.
Kind regards,
bg
Edits: 05/27/15
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