[CAUT] Measuring FAC (was Re: Re. Link to Young Paper)

[Jim Busby]

Dave,

 

I own an SAT and Verituner and at a class comparing ETDs Baldassin said
that the "other" ETDs have a fraction of a second delay to register the
note. He says this fraction is crucial and that he tunes to this "first"
part of the note. Do you find this to be the case? We compared tunings
with 4 ETDs and found that they all would "pass" the RPT test by 97
percent or better. 

 

Good to see I'm not the only one who turns off the ETD in the bass.

 

Regards,

Jim Busby

 

________________________________

From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of
Porritt, David
Sent: Monday, January 22, 2007 4:32 PM
To: College and University Technicians
Subject: Re: [CAUT] Measuring FAC (was Re: Re. Link to Young Paper)

 

Fred:

 

I no longer have an SAT.  I've found TuneLab to be easier to measure as
it's semi-automatic.  It needs 4 notes I use 6.  It does a good job.
Still, I tune from F3 - C8 checking things along the way.  When I tune
from E3 - A0 I turn off TuneLab when I get to the wrapped strings.  I'm
much more interested in smooth octaves than compliance to a particular
octave size (6:3, 8:4 whatever) or smooth progression of beat rates.  It
also helps battery life!

 

dave

 

David M. Porritt

dporritt at smu.edu

________________________________

From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of
Fred Sturm
Sent: Monday, January 22, 2007 4:55 PM
To: caut
Subject: [CAUT] Measuring FAC (was Re: Re. Link to Young Paper)

 

On 1/19/07 8:30 PM, "Jim Busby" <jim_busby at byu.edu> wrote:

Hi Fred,



At a convention someone mentioned this as "the" way one should take the
FAC measurements. Wasn't this in the journal once too? I'm still unclear
as to the "step by step" instructions. (1, 2, 3...) For the gadget
impaired, (me) would you give those instructions???



Thanks,

Jim Busby

Hi Jim,
    I am not aware of anyone teaching this particular method. I have
heard of a couple of different variants, at least one of which was
published in the Journal, but they were substantially different and for
different purposes.
    Here are step by step instructions:
1) Turn on SAT, press tune button. You are at A4, 0.0 cents. Tune the
string and stop the lights. (Side effect: WOW! You have tuned a string
to the pitch where you want to leave it).
2) Octave up to A6. Play A4 holding the measure button to stop the
lights (or do cents up, whichever you prefer, and whichever produces
more accuracy - maybe a combination).
3) Take that number and multiply it by 0.8. (Eg, 10.0 x 0.8 = 8.0).
Using the cents down button, move the display number to the resulting
number (Eg, from 10.0 to 8.0). Enter that number (Shift/Stretch) and the
display will now move to C6, 0.0 cents.
    (For ease in doing this in my head, I prefer to think of it as
reducing the number by 1/5. Divide the number by 5 and subtract that
from the total. And, hoping not to confuse the issue, an additional
mathematical trick to accomplish this is to multiply by 2 and then
divide by 10. So, eg, 11.7 x 2 = 23.4 / 10 = 2.3. 11.7 - 2.3 = 9.4. If
this seems like gibberish, ignore it. If it makes sense, use it.).

4) Now you are on C6 at 0.0. Tune C6 to stop the lights. 
5) Octave up to C8. Measure. I find it helpful to do cents up with the
cents up button to about 30 cents, then use the measure button (makes it
easier for the SAT to find the pitch). 
6) Take this result and divide it by 5. (Eg, 35.0 / 5 = 7.0). Octave
down to C7. Cents down to the resulting number. Enter that number
(shift/stretch). The display moves to F5, 0.0 cents.

7) Do F as usual. 
    But I'll comment a little on the F number, which, it seems to me, is
the weakest link in the FAC system. I find that it doesn't really serve
well for pianos that have high inharmonicity for F3. The major effect of
a high F number is seen in the bass, from A0 to B2, and high F numbers
will produce octaves that are too wide (IMO), especially for those
spinets to studios which have the highest numbers. 
    And, of course, it all depends whether F3 is wound or plain wire.
The scaling of a Hamilton is very close to that of an Acrosonic, except
the Hamilton has a plain F3 while Acrosonic has a wound F3. So the
Acrosonic's F number is a lot lower. There are lots of other similar
examples.
    Bottom line, I reduce high F numbers, usually to a nominal 10.0

8) "Across the break." As long as I've gone into this much detail, I'll
mention a bit about tuning across the break, meaning in pianos with a
big jump in inharmonicity between plain and wound strings. Sanderson
provides an article or two (or they did ten years ago) suggesting the
use of two tuning pages to smooth the tuning across the break. One
tuning uses the measured F number, the other uses a lower number derived
by measuring the top wound string, as I recall. The instructions are to
use the page with the higher F number for the plain wires, the lower
number for the wound strings. This does make for better octaves in the
tenor and bass (as I described above, in advocating for a lower F
number), but it does nothing to smooth the transition across the break,
defined as making the M3, M6, M10 beat rates progress more evenly. In
fact, the two tuning pages will have numbers that are identical in the
area across the break (or, at most, varying by 0.1 to 0.2 cents,
basically insignificant). 
    Bottom line, I'd advise not bothering. If you want to smooth the
break, I can give you a way to do it with a SAT. I'm not convinced
anyone but a tuner would notice. People notice the break, but not
because the M3s don't progress or have a little jog in beat rate. It's
because the inharmonicity changes, so the sound of the notes themselves,
and especially the sound of octaves and 5ths changes. And there is
nothing we can do about it in tuning the piano. The partial ladders line
up differently, and they are going to no matter what. Better to "let the
numbers fall where they may" and focus instead on unisons in that area,
IMO.

I hope this is helpful.
Regards,
Fred Sturm
University of New Mexico 

 

________________________________

From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of
Fred Sturm
Sent: Friday, January 19, 2007 4:47 PM
To: caut
Subject: Re: [CAUT] Re. Link to Young Paper



On 1/19/07 3:29 PM, "David Brown" <David.C.Brown.2 at asu.edu> wrote:

Dear Fred-

I wonder if you could expand on this a bit more. I attempted to
calculate FAC this way after reading your post but I must have done
something wrong. The difference between the first and fourth partial of
A4 seemed to yield a wider octave ( larger A number, to be expected I
suppose) than the normal reading,  but the difference between the first
and fourth partial of C 6 yielded numbers well into the 20's or 30's! I
tried the the difference between the first and second partial of C7 as
well and still no real usable numbers for me. There must be a way to
enlighten me! 


Hope all is well in New Mexico.

Regards-

David


Hi David,
    The A4/A6 difference needs to be multiplied by 0.8, to factor out
the difference between 1st and 2nd partial and leave the difference
between 2nd and 4th partial. The C6/C8 difference needs to be multiplied
by 0.2 to factor out the difference between 2nd and 4th partial and
leave the difference between 1st and 2nd partial. The difference between
1st and second partial is 1/4 the difference between 2nd and 4th partial
(it's a logarithmic scale, based on a square of the difference between
partial numbers, kind of).
    So, if you read A4/A6 as 10 (zero A4 and read its 4th partial at A6
as plus 10 cents), you enter 8 as the A number. When you have calculated
the tuning, the number for A4 (the tuning offset, tuning it's 4th
partial) will be 10. For C6/C8, if the number is 35 (C6 zeroed, its 4th
partial at C8 read as plus 35 cents), you enter 7. (Obviously when you
enter the number, you have to go to the right note name and octave, and
scroll cents up or down).
    Is this clearer? 
    (BTW, David is referring, I believe, to some posts I sent to
pianotech around ten years ago, when I was coming to terms with my SAT).

Regards,
Fred Sturm
University of New Mexico 

  

 

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