ETDs, PCs, PDAs & cellphones vs tuning fork : how accurate are they ?

[Robert Scott]

Philippe Errembault writes:

> Do you usually have an idea of the precision of the A440 reference
> you use ? I mean... I didn't get any the precision information with
> my tuning fork, I found it on the net.
>I wonder what are the precisions of professional ETDs, and what
> precision we can expect from a pocket PC, about which I wonder
> if it even can be as precise as a normal PC...

If you have back-issues of the PTG Journal you might want to take a look at "Calibration of Pitch References" in the August 2001 issue.  It shows that all major ETDs are calibrated to better than .01 cents. The article also discusses tuning forks, their temperature dependency and accuracy, and how to calibrate them.


> ...it might be that PDAs only contain ONE reference clock, for time,
> for CPU and for sound processing.

I have found that not to be true.  In fact, even on the Pocket PCs, they sometimes have separate audio sample rate oscillators for the listening mode and the sound-generating mode (recording and playback).  As for the CPU clock, that is definitely not tied to the audio clock because the Pocket PCs take advantage of switching to slower CPU clock speeds during idle times to save on power.  You can't have your audio processing clock tied to such a variable clock source.

It really does not matter that the audio sample rate is not precise, as long as it is stable.  Once you do a software calibration on your ETD, the results are the same as if the oscillator were perfect to begin with.


> There was also someone who claimed that listening a tone reference
> through a cellphone was as good as with a normal phone. I know the
> buffering of cell phone is small, but this doesn't change the fact that any
> shift in it's clock should be retrieved in the output!..

You can depend on the frequency of sounds being delivered accurately over the cell phone network.  There is no pitch distortion.  What is unclear is whether the same can be said for the Voice-over-Internet Protocol Internet services that deliver telephone service through your computer.  This is potentially subject to indeterminate TCP/IP buffering and perhaps pitch distortion.

Robert Scott
Ypsilanti, Michigan