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

[Philippe Errembault]

Hi Geoff,

The problem is not in trasmission. what you listen to are not bytes in a
buffer, but
the need to be re converted to analog sound. The problem is in the digital
to analog
conversion. Let's assume one use a sampling rate of 44 100 Hz, like on CDs.
you can
always calculate the samples instead of really recording them, so let's
assume the
recording was perfect. So a one second 440Hz tone, will contain 44100
samples which
will contain 440 period of a sine wave.

Now, imagine you play this sample on a sound device whose quartz is 1% too
slow.
the real play back will only play 44100-441 = 43659 samples during the first
second.
and so you will only play 440 * 43659/44100 = 440*99% = 435.6 periods of the
sine
wave during this second and so the frequency of your tone will be slowed
down to
435.6 Hz.

Please think well about it before saying I'm wrong, because I may be a
newbee in
tuning but I'm definitely _not_ a newbee in digital sound processing. ;-)

Philippe Errembault

----- Original Message ----- 
From: "Geoff Sykes" <thetuner at ivories52.com>
To: "'Pianotech List'" <pianotech at ptg.org>
Sent: Friday, May 26, 2006 6:54 AM
Subject: RE: ETDs, PCs,PDAs & cellphones vs tuning fork : how accurate are
they ?


> If the transmitting or storage medium of your source was analog then clock
> speeds, transfer, repeater and amplifier delays, and any number of other
> mishaps could indeed alter the frequency. Think speeding up or slowing
down
> a record player. (You do remember records, don't you?)
>
> Digital, on the other hand, is simply a collection of one's and zero's in
a
> very specific order. Regardless of clock speed, storage, transmission,
noise
> or any number of inconsistencies in the signal path, even if you
> deliberately change the speed the transfer process or processor clocks,
> those one's and zero's will ALWAYS arrive in exactly the same sequence in
> which they were sent. When they don't, the result is noise and dropouts,
not
> speed or frequency shift. In other words, a calibrated 440Hz tone sent
over
> a digital signal path will still be 440Hz at the receiving end. Changing
the
> pitch of a digital signal is possible, but it involves some serious and
> deliberate number crunching.
>
> Broadcast tones, ala WWV, I would not trust as absolutely accurate. Tones
> over the phone, unless you are absolutely sure there is no analog stage in
> the chain, I would also hold suspect. Also, once a digital signal has been
> converted back to analog it passes through amplifiers and a speaker so we
> can hear it. Unless those components are extremely high quality the end
> result might not be exactly spot on. But unless you have a precision
> frequency counter or a calibrated spectrum analyzer handy you probably
would
> not be able to tell. Just how accurate do you want to be? We're talkin'
> pianos here, not rocket science.
>
> -- Geoff Sykes
> -- Assoc. Los Angeles
>
>
>
>
>
>
>
> -----Original Message-----
> From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On
Behalf
> Of Robert Scott
> Sent: Thursday, May 25, 2006 6:59 AM
> To: pianotech at ptg.org
> Subject: Re: ETDs, PCs,PDAs & cellphones vs tuning fork : how accurate are
> they ?
>
>
> 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
>
>
>
>