When I first got my SAT, I calibrated my forks to be at exactly 440 when
at body temperature. I achieve this by tucking it between by belt and my
body for about two minutes. I still have one of those forks in a drawer in
my dresser, as a back-up. I check it once in a blue moon. It hasn't changed
by a tenth of a cent in eight years, according to my SAT, so I kinda get the
impression that the SAT isn't changing either.
I was under the impression that the SAT uses a quartz crystal, which can
only oscillate at one frequency. Let me know if you think I'm wrong.
Kevin E. Ramsey
ramsey@extremezone.com
----- Original Message -----
From: "Robert Scott" <rscott@wwnet.net>
To: <pianotech@ptg.org>
Sent: Friday, January 19, 2001 2:33 PM
Subject: Calibration of ETDs
> Electronic Tuning Device (ETD) users:
>
> While looking around for a better way to calibrate TuneLab, I have
> revisited the use of NIST services and it seems to me that this can
> be a practical means of checking the calibration of not only TuneLab
> but SAT and RCT as well.
>
> The services I refer to are the 500 Hz and 600 Hz standard tones
> available on shortwave radio and by telephone at (303)499-7111 (Colorado).
> Leaving aside the shortwave option, since most techs do not have access
> to shortwave radios, I would like to consider the use of the telephone
> service. The number is not toll-free, so it is wise to plan your
> use of this service carefully. NIST says this is a very popular number.
> They get over 2,000,000 calls per year. When you call this number,
> you will hear the WWV broadcast. If you can get your computer or the
> SAT to pick up the sound from the telephone receiver, then you can check
> calibration. Try holding the telephone right up to the microphone. Before
> you call, try to get the dial tone to register on your ETD just to
> see if the phone is loud enough. You will want to figure out how to
> place the phone on the ETD's microphone so that it will stay put without
> your hanging on to it and causing noises that will interfere with
> the pickup of the tones.
>
> In order to be sure of hearing a 500 Hz or 600 Hz tone when you call,
> check the following broadcast schedule, which is repeated every hour.
> When a tone is present, it is present for the first 45 seconds of the
> minute and is silent for the last 15 seconds. As you can see, the
> best time to call is between 19 and 24 minutes after the hour, or
> between 30 and 39 minutes after the hour.
>
> Minute Contents
> 0 station ID
> 1 600 Hz tone
> 2 (440 Hz tone)
> 3 no tone
> 4 no tone
> 5 600 Hz tone
> 6 500 Hz tone
> 7 600 Hz tone
> 8 storm warnings
> 9 storm warnings
> 10 storm warnings
> 11 600 Hz tone
> 12 500 Hz tone
> 13 600 Hz tone
> 14 GPS reports
> 15 GPS reports
> 16 OMEGA reports
> 17 600 Hz tone
> 18 Geoalerts
> 19 600 Hz tone
> 20 500 Hz tone
> 21 600 Hz tone
> 22 500 Hz tone
> 23 600 Hz tone
> 24 500 Hz tone
> 25 600 Hz tone
> 26 500 Hz tone
> 27 600 Hz tone
> 28 500 Hz tone
> 29 no tone
> 30 500 Hz tone
> 31 600 Hz tone
> 32 500 Hz tone
> 33 600 Hz tone
> 34 500 Hz tone
> 35 600 Hz tone
> 36 500 Hz tone
> 37 600 Hz tone
> 38 500 Hz tone
> 39 600 Hz tone
> 40 500 Hz tone
> 41 600 Hz tone
> 42 500 Hz tone
> 43 no tone
> 44 no tone
> 45 no tone
> 46 no tone
> 47 no tone
> 48 no tone
> 49 no tone
> 50 no tone
> 51 no tone
> 52 500 Hz tone
> 53 600 Hz tone
> 54 500 Hz tone
> 55 600 Hz tone
> 56 500 Hz tone
> 57 600 Hz tone
> 58 500 Hz tone
> 59 no tone
>
> In order to use the 500 Hz and 600 Hz tones to check your pitch
> calibration, select a no-stretch tuning. If your ETD uses the
> fundamental to tune C5 and D5, then customize the stretch for those
> two notes so the C5 is stretched -78.69 cents and D5 is stretched
> +36.95 cents. Save these customizations in a tuning file or a page
> in the SAT memory. These stretches will make C5 exactly 500 Hz and
> D5 exactly 600 Hz. If you want to use the standard SAT partials,
> then use C3 and D3 instead. The SAT uses the 4th partial to
> tune these notes and so you will again get 500 Hz and 600 Hz if you
> use the stretch numbers shown above.
>
> Once you have the ETD all set up to look for 500 Hz and 600 Hz on
> C and D, then call the Colorado number at a time when you
> can be sure of hearing the desired tones. You will only have three
> minutes maximum because they automatically disconnect you after
> three minutes. With the tone sounding in the microphone of the ETD,
> select either the C or D depending on which tone is playing. Having
> the stretch numbers preset in memory makes it easy to switch between
> 500 Hz and 600 Hz quickly. Once you determine which tone is playing,
> note the rotation of the lights in the SAT or the spinner in the RCT
> or the movement of the squares in TuneLab. Any movement in these
> displays indicates the error in calibration. If you can adjust the
> offset to make the display stand still, then that offset tells you
> exactly how far off your ETD is.
>
> When checking the SAT, you will be limited to one decimal place
> in setting the stretch. How much will that affect the results?
> Well, if you set D5 (or the 4th partial of D3) to a stretch of
> +36.9 instead of +36.95, that difference of .05 cents will mean
> that a perfectly calibrated SAT listening to a perfect 600 Hz
> ought to indicate sharp by .017 beats per second, which means the
> lights in the SAT ought to rotate one light clockwise in 14 seconds.
> This is barely recognizeable in the 45 seconds during which you
> can observe the 600 Hz tone. And what about the C5 offset by
> -78.7 cents instead of -78.69 cents? This error of .01 cents when
> listening to 500 Hz means the SAT should indicate sharp by .0029
> beats per second, which means the lights ought to rotate one light
> clockwise in 86 seconds - definitely not detectable during the
> 45 seconds of 500 Hz tone.
>
> When checking the RCT, I'm not sure whether you can actually
> refine your calibration or just check it with this method, since
> Dean supplies a calibrated 440 Hz source to perform the initial
> calibration.
>
> When checking TuneLab you can trim the offset until the phase
> display is absolutely stopped and then enter 500 or 600 in the
> New Calibration menu. Then you can say that your calibration
> is traceable to NIST, the most precise reference that there is.
>
> And if you do have a shortwave radio, try picking up WWV on
> 2.5, 5, 10, 15, or 20 MHz and save yourself the phone call.
> However, I have had great difficultly getting a reliable signal
> during the day in Michigan. It works better at night.
>
> -Rober Scott
> Ypsilanti, Michigan
>
>
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