Frequency accuracy?

[Frank Cahill]

Clark Sprague wrote:
> 
> List, I too have been wondering just what is accurate.  My SAT reads
> my Bechstein fork at approx. 1 1/2 cents flat.  I assumed that the
> fork that went with such an expensive instrument would be accurate.
> And my SAT was calibrated and re-worked with new boards less than 1
> year ago.
> Clark Sprague
> Greenwich, Ohio
> 
> Brian Trout wrote:
> 
>       Hi, I have been tuning aurally for most of the time I've
>      tuned.  When I first started out, I got a chrome plated
>      steel tuning fork.  It's not very loud, but it seems to be
>      pretty stable.  I've heated it up to well over 100 degrees,
>      and put it in the freezer to cool it down, and measured as
>      best I could in both extremes.  It doesn't move much,
>      perhaps 1 or 1 1/2 cycles from one end of the extreme to the
>      other.  (It's hard to measure, because it starts changing
>      back to room temperature before I can really get some good
>      "listens".) At work amongst the tuners, we have 3 tuning
>      forks, and 3 "machines", none of which are over about $200
>      machines.  My personal observations to date lead me to
>      believe that the forks are all very close to each other.
>      However, the machines are quite different, one of which
>      actually tunes a piano sharp enough to hear audible beating
>      when played with another piano tuned with a fork.  (This is
>      when you're trying to set the pitch at A-440.) My question
>      is, how does one determine which A-440 is right?  Is there
>      an easy way to do that without finding an electronic
>      frequency counter?  I can't think of anyone who has one.
>      I'm just trying to figure out if real tuning fork accuracy
>      is possible in a real world.  To what do we pay homage as
>      the "ultimate" standard measuring device?  Who's "ultimate"
>      standard measuring device is right if they don't agree???
>      If I find one person with an SAT and one with an RTC and the
>      A-440's aren't the same, who's right? I'm not trying to be
>      obnoxious here, but I've been reading about the "big test",
>      and what's involved.  It all starts with the basic premise
>      that we start at A-440.  It's been worrying me a bit.  Who's
>      A-440? Any thoughts out there? Brian TroutQuarryville,
>      Pa.btrout@desupernet.net
> 
> 



As a former electronic engineer and current ham radio operator, I know
that electronic gear has to be checked, or calibrated, from time to
time.  There are calibration labs that do this kind of work. These labs
calibrate their equipment to a known standard that can be traced back to
the bureau of standards (now call NIST). This is the ultimate frequency
standard.

I have two accutuners and a single accufork. The accufork, which is an
electronic pitch fork, reads 440Hz on both accutuners. That's a good
indication that all machines are working properly.

The accutuner is a high-end device, designed by a competent engineer to
rather tight standards.  Those $200 machines are not in the same
category. They are not suitable for piano work. Only accutuners, RCT,
and perhaps yamaha's PT100 are suitable. I've not seen the new Peterson
scopes, so I can't be sure about those.

I suspect that if you put a cybertuner next to an accutuner, they will
be very close if not exactly the same.

When I take my tuning exam, I'll have my accufork. I know I can trust
it's frequency.  
-- 

Frank Cahill
Associate Member, Piano Technicians Guild
Northern Va