[pianotech] False Beats and Changing Beat Rates

[David Love]

#4 might be that an irregular termination point causes a slight shift in the
pitch from the early to the late phase due to the changing excursion
characteristics of the string.   

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Albert Picknell
Sent: Thursday, February 03, 2011 5:27 PM
To: Pianotech List
Subject: [pianotech] False Beats and Changing Beat Rates

Hi List

Okay, so I'm tuning a single treble string that has a false beat, let's say
E6 (the other two strings of that note are muted off).  I play the E6 with
C4 a major 17th below, and listen to the beat.  The beat starts off very
rapid, but gradually slows down as the notes decay.  Is anyone aware of any
explanation that has been given for this phenomenon?  I assume the
phenomenon has something to do with the presence of false beats, because I
only hear it when false beats are present.

I can think of several possible explanations:

#1. The false-beating string is actually dropping in pitch as the tone
decays.

#2. The strings of the lower note (in this case C4) are actually rising in
pitch as the tone decays, whereas the upper string with the false beat does
not rise in pitch.  I doubt this is the correct answer, because the slowing
of the beat rate occurs during a portion of the tonal envelope during which
an ETD does not show the lower note rising in pitch.

#3. The slower beat rate heard after a period of decay (when the false beat
seems to have faded somewhat) is the true beat rate.  During the earlier
phase of the tonal envelope, when the false beats are more prevalent, some
interference pattern is happening that causes the beat rate to sound faster
than it really is.

#4. I can't think of a #4.

Cheers,
Bert