Overpull

[Mike Kurta]

Can I add 2 cents (ha)....   I have used a Korg AT-120 for pitch raising for
several years and find it very useful.  It tells me where each note is
BEFORE I tune, and using a sliding scale from 20 to 35% over or underpull,
it comes out very close.  An additional advantage is easily showing the
customer how far out of tune their instrument is at this time.  By
reinforcing the need for regular tunings, the message is conveyed in a more
positive manner.  Mike Kurta
----- Original Message -----
From: "Robert Scott" <rscott@wwnet.net>
To: <pianotech@ptg.org>
Sent: Friday, March 29, 2002 8:44 AM
Subject: Re: Overpull


>
> When we speak of calculating overpull using 25% or 30% or whatever, it
> is important to consider what the 25% or 30% applies to.  Nearby notes
> have a larger effect than notes that are slightly farther away.
> Therefore the correct overpull depends on how much pitch change there
> will be in the notes we are going to tune after the current note.
> Ideally, we would like to look ahead and learn how flat are the notes
> we have not tuned yet, because they will affect the settling of the
> current note.  But that is not practical.  Instead we use the recent
> history of flatness as a predictor of how flat the upcoming notes will
> be.  Here is where the various tuning devices use different methods.
>
> RCT, as far as I know, uses a moving "boxcar" average.  That is, the
> history of the last N notes is averaged to arrive at the estimate of
> how flat the piano is in the region of the current note.  As you move
> up the scale, the contribution from the most distant note drops out
> of the average as a new note is added in.  But all notes in the
> average participate to the same extent.  This gives equal weighting
> to the most recent note and the most distant note in the average.
>
> TuneLab, on the other hand, uses a declining weight average.  The
> most recent N notes are combined in a weighted average.  The
> weighting given to each note is the most for the most recent note
> and it declines linearly to zero for the most distant note.  In
> this way the notes participate in the average in proportion to
> how recent they are.  The most recent notes have the greatest
> effect.  This is done to develop an average that responds
> more quickly to changes in flatness as you move up the scale.
>
> Both TuneLab and RCT allow adjustment of the number of notes
> that are used to form the average.  Then the overpull percentage
> is applied to this average to calculate the overpull amount in cents.
>
> Perhaps Dave would like to enlighten us on how the VT forms its
> average in pitch raise mode?
>
> And Bradley, you have been asking some very interesting questions
> lately - about arcane aspects of inharmonicity and overpull.
> One might suspect you are developing a tuning program of your own?
>
> -Robert Scott
>   Real-Time Specialties
>