On 2013-01-28 23:04, unruh wrote:
On 2013-01-28, Jeroen Mostert<jmost...@xs4all.nl> wrote:
On 2013-01-27 23:43, unruh wrote:
On 2013-01-27, David Taylor<david-tay...@blueyonder.co.uk.invalid> wrote:
On 27/01/2013 19:33, unruh wrote:
On 2013-01-27, no-...@no-place.org<no-...@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
Not really. A cent is simply 1/100th of a semitone, no more, no less. It's true
that few if any should be able to distinguish a note from a note that's one cent
off when heard in isolation, but the cent is not some sort of biological limit,
as far as I know. When played together, a difference of one cent between notes
is certainly audible in the beating (at least on artificial waves, I have no
idea if the same is true for physical pianos). Whether you can even physically
tune a piano that accurately is another matter altogether. Even if you can't,
you should still like to be able to tell that you didn't.
at 440 Hz, 1 cent is a frequency difference of .25Hz -- ie 4 sec, and
the piano note dies out faster than that.
So for two pianos sounding together, the beating shouldn't be audible. OK.
Also the various strings in a note ( remember that pianos have 2 or three
strings per note) cause frequency difference of greater than that. The higher
harmonics for which the beating would be faster (eg 4th harmonic would have a
1 Hz beating,) are also "out of tume"-- ie the 4th mode is not 4 times the
fundamental, on a piano but slightly greater.
So the beating *should* be audible. OK. :-)
And who "should you still like to able to tell that you didn't"? A piano
tuner is there to make the piano sound good, not to engage in
unwarrented mathematical games.
Well, then, why measure at all? As long as it sounds good.
Surely to make it sound *as good as possible*, you need to be able to accurately
measure how close you got to your goal. If you are able to tune a piano to
within 1 cent (or thereabouts, granting that it may be difficult), you need to
measure better than 1 cent to know how good your tuning actually is.
Even if you consider accurate detection of 1 cent to be good enough for tuning
purposes, your measuring equipment still needs to be an order of magnitude
better. A 0.1 cent difference is 57.8 ppm. 12 ppm is 0.02 cent, which isn't
excessive if you're going for 0.2 cent accuracy.
?? And if you are going for 10^-12 cent accuracy it is horrible. But why
would you be going for .2 cent accuracy?
Don't ask me. Ask the piano tuners. Unless you *are* one, of course. In which
case it sounds like you have to educate your fellow practitioners.
--
J.
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