[time-nuts] Clocks for Audio gear

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Fri May 11 07:48:30 UTC 2012


Ashihara's tests were with music/voice, taking into account 
psychoacoustics, for an average group of music savvy listeners, and even 
music professionals.
As uncorrelated jitter is practically raising the noise floor, most of 
it was masked by the signal, making it more difficult to detect. 
Benjamin and Gannon used sinusoidal jitter, which isn't appearing 
normally in signal chains (badly designed ones excepted).
In a real case, with higher probability (added) jitter would be 
correlated with the digital content transmitted over a path - S/PDIF, 
and AES/EBU are prone to jitter induced by the signal path 
characteristics, ISI - PSUs, and even external noise sources.
A more realistic simulation would take those into account.
OTOH there where tests on pure sine tones, with sine jitter, detectable 
by trained ears at even lower levels of jitter, which might indicate the 
lowest threshold of hearing, but using artificial conditions.
Who would listen to pure sine tones?

On 5/10/2012 8:25 PM, Heinzmann, Stefan (ALC NetworX GmbH) wrote:
> Chris Albertson wrote:
>> If we are to believe the above paper,then those guys who claim to hear
>> pS jitter are wrong.
>
> Note that the jitter spectrum matters for its audibility. Ashihara et.al. used random jitter, and it is not very suprising that the sensitivity for random jitter is lower than for jitter that has specially been shaped to improve detectability by human ears. Thus the results by Ashihara are credible, but they are not the lower limit on jitter audibility.
>
> Benjamin and Gannon, the first reference in Ashihara's paper, come to lower figures for sinusoidal jitter with carefully selected frequencies relative to the main signal, which is also sinusoidal. Their results reach down to the single figure nanosecond range, and that can be regarded as the real limit of audibility.
>
> Of course, that still leaves those who claim to hear jitter in the picoseconds range out in fairy-tale land. And jitter of just a few nanoseconds is still quite easy to achieve with crystal oscillators. No need for special and expensive parts, then. Normal developer diligence is enough.
>
> Cheers
> Stefan
>
>
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