[ntp:questions] Using NTP to calibrate sound app

unruh unruh at invalid.ca
Sun Jan 27 22:43:06 UTC 2013

On 2013-01-27, David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> On 27/01/2013 19:33, unruh wrote:
>> On 2013-01-27, no-one at no-place.org <no-one at no-place.org> wrote:
> []
>>> In case you are wondering, my app is a professional piano tuning app.
>>> The standard in this industry is that tuning devices should be
>>> accurate to 12 parts per million.  I know that is probably overkill
>>> for tuning pianos, but that is what the professionals expect from
>>> their equipment.
>> Ah. I would expect 1 cent, which is more like 500PPM.
> 1% (10,000 ppm) is a 4.4 cycles per second beat at 440 Hz!  Completely 
> unacceptable.  You want an imperceptible beat, ideally, well under 1 Hz. 
>   Agreed that 12 ppm is overkill.

I agree that 1% is pretty bad-- that is 1/6 of a semitone, which is
clealy preceptible. However 1 cent, 1/100 of a semitone, is the limit of
audibility, and it is VERY hard to tune a piano string to 1 cent (pin
slippage and adjustment, frequency coupling between the various strings which play the
same note, anharmonicity of the string)-- it is not even clear what that
means for the above reasons. 1 cent (NOT 1 percent-- a cent is 1/100 of
a semitone) is about 1.0006 frequency ratio (.06%).

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