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In Reply to: RE: Some kind questions about reclocking posted by Thorsten on January 27, 2015 at 05:45:28
Hi and thanks sincerely for the very interesting explanation quite beyond my ability to understand sadly
But my question was very very basic
If i am not wrong the very reason of reclocking is to reduce the influence of the transport on the overall sound
So if a dac that reclocks, when well designed and built of course, is used with different transports it should give a very similar sound.
If not it reclocks badly just that.
By the way i stop here ... i will try with different sources and listen for any change in sound.
Thanks again.
Kind regards,
bg
Follow Ups:
The term "re-clocking" has been commonly used to describe decidedly different jitter reduction methods. Some DACs utilize a technology called Asynchronous-Sample-Rate-Conversion (ASRC), which alters the original sample amplitude values in order to effectively filter jitter from the incoming signal. This is more correctly called a re-sampling technology than it is re-clocking. ASRC does produce two independent clock domains, that of the incoming data signal and that of the re-sampled outgoing data signal. The outgoing data signal is usually timed by a fixed crystal controlled local (located within the DAC box) clock generator, which probably why it is often termed re-clocking.There are other entirely different jitter reduction methods which do not alter the original sample values, yet still produce two nearly independent clock domains. These circuits typically utilize a specialized memory function known as an asynchronous FIFO, and some form of adjustable crystal controlled local clock generator. A DAC box might internally contain one or none of the above two highly effective jitter reduction technologies. In addition, there is yet another common meaning for the term re-clocking, wherein a new clock domain is not created. The data and any synchronously derived clock signals are simply re-aligned to whatever is the existing local clock domain.
In short, the term re-clocking doesn't by itself conclusively tell you whether effective jitter reduction is employed. In addition, we haven't even touched on the jitter that noise conduction across the transport to DAC digital signal interface can induce. A unusally well engineered DAC digital signal interface, such as Thorsten describes, can effectively cure all these problems, however, such is far from common.
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Ken Newton
Edits: 01/27/15 01/27/15 01/27/15 01/27/15 01/27/15 01/27/15 01/27/15
Hi and thanks a lot for the very valuable explanation
But this is difficult. I think that in the end the only way for me is to try and listen ... with patience and good luck.
I understand that there are so many variables that can have a remarkable impact on the final sound.
Thank you sincerely anyway for the interesting advice.
Kind regards,
bg
Hi,
> The term "re-clocking" has been commonly used to describe
> decidedly different jitter reduction methods.
Thank you. This is what I wanted to bring out.
There is no clear definition here.
If I am taking the System Clock from the SPDIF receiver (which is PLL derived from the data and usually high in jitter) and the use this clock to re-clock the signals to the DAC Chip, before they enter the DAC Chip I can claim "special re-clocking".
Of course, it will not lower the transfer of source jitter and so it will not make the DAC less sensitive to source jitter, even though it may, in practice improve the sound quality of the DAC nevertheless (or make it worse, as such things may be).
On the other hand, what I showed is a case where a new FFL (not PLL) is used to create a new clock that is very low in phase-noise (in practice close to the phase-noise of the crystal oscillator serving as reference for the FFL) and is normally completely static in frequency once locked (I find several minutes between each clock update, which is normally a singe 40ppb (parts per billion) step.
So as long as the actual receiver can lock onto the source stream the re-clocking system removes all source jitter from the SPDIF stream. That too could be called "special re-clocking".
So it is definitely worthwhile understanding exactly what sort of re-clocking technology is employed, rather than to just take the ad-copy and say: "Oh re-clocking - good, now I do not need to worry about crappy sources"...
Because, you might still have to after all.
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?
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