[time-nuts] Clocks for Audio gear

Henk henk at deriesp.demon.nl
Fri May 11 11:58:24 UTC 2012


Hi,

That jitter value, was that one period jitter? Or was it jitter over a
large number of periods, thus close by the carrier?

Henk

> MailLists wrote:
>> 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?
>
> Ashihara et.al. wanted to find out what level of jitter was likely to be
> audible under real-world conditions. Those conditions would likely include
> music as the main signal, and random jitter.
>
> Benjamin/Gannon wanted to find out what levels of jitter could be detected
> if the conditions were as favorable as possible for detecting jitter. That
> is not the real-world situation, of course, but it can establish a
> baseline where you may legitimately say that if you stay below this line
> with jitter of whatever type, the effects are very unlikely to be audible.
> And, to add a comment towards Attila, one of the results by
> Benjamin/Gannon was that training matters a lot, and the best sensitivity
> was by trained listeners. Your comment is therefore warranted, but already
> accounted for.
>
> Hence, even though their results appear to be very different, they are
> both valid, because it depends on the exact question asked. I would dare
> to say, that no matter how you set up your "realistic" simulation, the
> results are likely to be somewhere between the values by Benjamin/Gannon
> and by Ashihara et.al.
>
> So, for the purpose of this group, I'd say the psychoacoustic stuff would
> lead too far, but it might be helpful to know at which jitter levels one
> can assume to be on the safe side in an audio system, regarding audibility
> of jitter effects. Judging from the mentioned studies, I concluded (for
> myself at least), that this boundary is somewhere in the single figure
> nanoseconds, until someone comes forth with hard evidence that it needs to
> be set lower.
>
> Cheers
> Stefan
>
>
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