On 2013-01-28, Jeroen Mostert <[email protected]> wrote: > On 2013-01-27 23:43, unruh wrote: >> On 2013-01-27, David Taylor<[email protected]> wrote: >>> On 27/01/2013 19:33, unruh wrote: >>>> On 2013-01-27, [email protected]<[email protected]> 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. 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. Also, the piano pegs have a pretty coarse adjusting mechanism-- static friction significantly higher than dynamic, so you tend to get stick-slip, making extremely fine admustments in the tension hard. 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. > > 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? > _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
