Unison coupling

[Jim Coleman, Sr.]

Hi Ron:

In your comment below about the pitch rise which you noted as dropping
in about a half second I believe is just the normal pitch drop which
we have been talking about for some time.

If you have occasion to borrow a SAT, you can play a note repeatedly
(perhaps 4 blows per second) then you can isolate the prompt pitch
and actually measure it. 

Someone asked about what you meant by attack phase and dwell phase. I
like to compare this to the decay graphs which we have seen on
oscilloscope pictures of piano tones. I prefer to call this the prompt
sound or tone during the first half second or so. With good voicing
techniques, we try to extend this initial body of the tone as long as
possible. But, of course we know that everything which goes up, must
come down. In voicing, we like it to come down slowly. For those on the
list who are not familiar with the decay curves, I'll try to imitate
one or two with ascii art below:
      x
    x    x

                                     This curve has a rather short
                                     peak and decay
  x          x
  



 x                 x

                        x
                               x
                                           x
x                                                                   x 




        x x
     x        x 
      
                                            This curve has more body       
   x                x                       during the prompt sound 
                                            and the decay is a slower
                                            descent. This tone has
                                            more "carry" to use a
  x                           x             Steinway term.
      


 x                                             x



x                                                                        x


The pitch change we can measure follows a somewhat similar curve. To
measure the extremes of the possible pitches of a string, play the note
with fast repetitions and measure the highest pitch you can see on the
ETDs. Then Pluck the string faintly to see the lowest possible pitches.
It is surprizing to see the differences. The light plucking adds less
tension to the string, hence the lower pitch.

Back in the 60s when I did a lot of measuring of inharmonicity of piano
strings, I decided that plucking the strings would give the most
consistent results because when striking the string the pitch was changing
too rapidly to get consistent results due to the moment in time that the
measurement was taken. All of these measurements were done in an anechoic
chamber using the StroboConn (twelve window job). In those days, we were
measuring only to a 1 cent tolerance, but the changes were still noticeable.
Today with instruments that can measure .1 cents quite accurately, the
problem is still: At what point in time are the measurements made and at
what amplitude? Then, when it comes to trying to tune within .01 cents,
as I pointed out in a Journal article about a year ago, this is ridiculous.
We can only measure accurately to .1 cents if we have a controlled key
striking mechanism and an accurate device for measuring the time of the
measurement. Piano tones are very transient as you can see from the above
ascii curves.

Jim Coleman, Sr.




On Mon, 24 Jan 2000, Ron Nossaman wrote:

> >Hi Ron, 
> >Sorry, I don't know what you mean by "pitch drop from
> > the attack phase to the dwell."  
> 
> * Sorry Ric, I don't have any other way to explain it other than how I
> already have. Perhaps someone else will take a crack at it.
> 
> 
> > Does the "pitch drop from the
> >attack phase to the dwell" need a "tool"  to be measured?  
> 
> * Apparently so. You hear the attack phase as noise. So do I, for the most
> part. ETDs show a higher pitch in the first half second or so, during that
> period where the tuner is mostly waiting for the "noise" to dissipate so he
> can get on with it. I often tune unisons by listening in that attack phase
> and hitting the key rapidly. It may sound like noise just listening to it,
> but when you try tuning in the first half second of the attack, you'll find
> that it's pretty well organized noise.
> 
> 
> >If so,
> >how does that measuring tool stand up to other measuring tools? 
> 
> * Which other measuring tools? Personally, I haven't made direct
> comparisons between all such available tools. Even if I had, and having
> chosen what I considered the best of the lot, I still couldn't prove it was
> "right". Let's ask around among the list folk and find out if users, or at
> least owners, of all the available ETDs register a pitch rise in the
> attack. Correct me if I'm wrong, but I don't think all the machines out
> there work by exactly the same method, so similar results among the
> machines ought to constitute acceptable evidence, at least for me. If
> that's not good enough, you can probably pick up a reasonably decent
> oscilloscope for less money than a high end ETD costs and find out for
> yourself. I, for one, would certainly be interested in hearing about what
> you come up with.
> 
> 
> >	A wild hunch suggests that "attack phase" is mostly noise, from
> >transitory shock waves resulting from the moment of impact of the
> >hammer, lasting milliseconds until the frequency of oscillation of
> >the piano wire is established. ---ric
> 
> * Entirely possible, but the pitch rise I measured in one string in octave
> 5 took about a half second or so to drop to the dwell frequency, not a few
> milliseconds.
> 
> 
> Ron N
>