[time-nuts] Clocks for Audio gear

[Jim Lux]

On 5/10/12 11:36 AM, Hal Murray wrote:
>
> albertson.chris at gmail.com said:
>> I've alway have thought that if nanosecond level jitter is "bad" then
>> breathing while listening must be really bad.  If you inhale the path length
>> from your ear to the speaker changes at the microsecond level.
>>   You'd think the resulting doppler shift would drive these audiophiles nuts.
>>   All that pitch shifting.
>
> Perhaps the spectrum of the "jitter" matters.  If the frequency is low
> enough, I call it wander rather than jitter.  Audio doesn't need DC or low
> frequencies so wander is easy to filter out with a simple high-pass filter.
>
> Heartbeats may be more interesting than breathing.  Does anybody know of
> spectrum domain data?  It should be possible to collect position info while
> also monitoring heartbeat and chest diameter and then crunch some numbers do
> see how much of the position correlates with heartbeat vs breathing and then
> plot each part in the frequency domain.
>
>


oddly, I happen to have just that data to hand, having been looking at 
ballistocardiography.  If you put someone in a bed, suspended by 4 wires 
(one at each corner), your heart beat results in about 1mm displacement 
(head to foot).  1 degree phase shift at 1 kHz, or thereabouts.


in terms of displacement in general, breathing is on the order of 1cm 
(at 0.1 Hz) and heartbeat is on the order of 0.1-1mm, depending on where 
you look.  (look up "microwave cardiography" for instance)