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haroon
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dCS Puccini U-Clock

Can somebody help me understand what does the widening/broadening of central peak, representing the 11.025kHz tone explains/means in the jitter test of dCS Puccini U-Clock?

I have been noticing this phenomenon in all jitter tests where USB was the digital input, e.g. Wavelength Cosecant v3 USB DAC (fig. 12 & 13 of measurement section), Ayre Acoustics QB-9 USB DAC (fig. 14 of measurement section), Musical Fidelity V-DAC (fig. 10 of measurement section). In all cases central peak, representing the 11.025kHz tone is actually two spikes at either side of actual 11.025kHz that are meeting at the top.

Whereas when S/PDIF was the digital input, central peak, representing the 11.025kHz tone, is thick but narrower and never split into two spikes except at bottom, e.g. Bryston BCD-1 CD player (fig. 9 of measurement section), Boulder 1021 disc player (fig. 10 of measurement section), dCS Scarlatti DAC (fig. 16 of measurement section), Lavry Engineering DA2002 D/A processor (fig. 11 of measurement section).

Editor
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Re: dCS Puccini U-Clock


Quote:
Can somebody help me understand what does the widening/broadening of central peak, representing the 11.025kHz tone explains/means in the jitter test of dCS Puccini U-Clock?

The broadening of the single peak (not a double peak, please note; this is a visual illusion due to the fact that the top of the graph is -70dBFS, not 0dBFS) is due to the presence of low-frequency, probably random noise-like variations in the clock frequency.

John Atkinson
Editor, Stereophile

haroon
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Re: dCS Puccini U-Clock

Hi John:

Thank you for the help; you have been a very kind editor, always come forward to help us even on the face of all the opposition.

From your post what I understand is that the visual thickening/broadening of the central peak, representing the 11.025kHz tone, perhaps

Represents the time accuracy of clock oscillator that manufacturer markets as,

Editor
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Re: dCS Puccini U-Clock


Quote:
However, the question remains that why such thickening/broadening of the central peak is more prominent as to become split when USB is digital source than other sources, say S/PDIF.

Presumably because there are still random low-frequency variations in the recovered clock for USB-derived data that are not present with S/PDIF data. I woudn't be concerned about this - USB audio data decoded by the Puccini and U-Clock produced possibly the best sound quality I have heard for computer-sourced audio in my system (along with the Ayre QB-9).

John Atkinson
Editor, Stereophile

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