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<DIV><FONT face=Arial size=2>Sarah, you're on! I've been in =
electronics
all my adult life. I also have a strong interest in sustain. =
Let me
think about your proposal a bit and I'll get back when I have a =
moment.
The first order of business is to define sustain. Can't measure it =
if is
isn't defined. I'll post later about some of the problems I see =
over the
hill. Thanks.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Peace to you too!</FONT></DIV>
<DIV><FONT face=Arial size=2>Carl Meyer Assoc. PTG<BR>Santa =
Clara,
California<BR><A href="mailto:cmpiano@attbi.com">cmpiano@attbi.com</A> =
</FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>
<A title=sarah@gendernet.org =
href="mailto:sarah@gendernet.org">Sarah Fox</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A =
title=pianotech@ptg.org
href="mailto:pianotech@ptg.org">Pianotech</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, November 20, =
2002 10:25
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Electronic Sustain =
Timer</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial size=2>Hi all,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I thought more about how to time =
sustain while
taking my morning shower (ordinarily a very productive time for =
me). It
occurs to me that the best way to do it is electronically -- with a =
simple
circuit made just for that purpose. Many of you work at =
universities,
and you could probably find a departmental electronics technician who =
could
put together such a circuit on a breadboard in no more than an hour or =
two. Some of you may know enough about electronics to do it
yourselves. As for myself, I once maintained an electonics test =
bench
and designed/built these sorts of circuits, but I've been downsizing, =
and most
of that stuff is either given away or stored in boxes. I won't =
be able
to do this in the forseeable future.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Anyway, here's a description of the
circuit. This is very elementary stuff, and any electronics tech =
should
know how to put these circuits together out of no more than a few =
dollars in
parts (not counting the breadboard, which you would =
borrow):</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>There would be two op-amp circuits =
with 100-fold
(40 dB) differences in gain. Inputs to both would be =
capacitively
coupled from the same microphone. (An adjustable-gain preamp =
circuit
would be nice here.) Outputs from the two amps would be
capacitively coupled to two unity gain op amps ("voltage =
followers."
Outputs from the voltage followers would then be quarter-wave =
rectified and
low-pass filtered, so as to yield an approximately DC output. =
(i.e.
diode, serial with resistor, feeding to one lead on a capacitor, with =
the
other lead grounded). Although this voltage wouldn't be RMS, it =
would be
"similar" and would summate energy not only only from the =
fundamental but
also from the harmonics. Those who want true RMS can possibly =
find
specialized V^2 amplifiers, but that's a bit
expensive/weird/exotic. Feed the outputs of those circuits to =
two
comparator circuits that would detect a voltage threshold. =
(Assuming the
100:1 gain is accurate, the threshold voltage should be the =
same for both
the high- and low-gain circuits.) Finally, feed the outputs of =
the
comparators to logic circuit that would output H when the high-gain =
circuit's
output is H and the low-gain circuit's output is L. This =
could be
done with an XOR chip, I think. Use this output to trigger a =
millisecond
timer (e.g. an old Hunter, probably available for loan from the junk =
pile of
any dept of psychology).</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>How to use it:</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>(1) Hook a soundboard mic to the =
circuit's
input. To avoid constructive/destructive interference effects, =
mute two
of the three unisons of the note being tested, both in the main *and* =
duplex
sections.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>(2) Play a note loudly enough to =
exceed the
low-gain circuit's threshold (loudly enough that the timer =
won't run
immediately.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>(3) As the amplitude falls, the =
output signal of
the low-gain circuit will fall below threshold, and the timer will =
start
running. The sound may "warble" a bit over the threshold, =
resulting
in the timer starting, stopping, starting, stopping, and then =
running.
That's OK, because the same thing will happen when the timer shuts
off.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>(4) As the amplitude falls further, =
the
output signal of the high-gain circuit will also fall below =
threshold,
cutting off the timer -- again probably with some warbling, which is
OK.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>(5) The 40 dB decay time can then be =
read in
ms. Assuming a linear falloff (and I don't know if this is a =
valid
assumption), the 6 dB falloff (i.e. amplitude half-time) would the 40 =
dB decay
time divided by 6.67. If decay is nonlinear, then just report =
the 40 dB
decay and try to reference it to some initial SPL value. With =
regard to
SPL, 99% of the world has no clue that an SPL reading is utterly =
useless
unless it is referenced to a distance from the sound source. =
Owing to
the "large" sound producing area of the piano and the complex nature =
of its
acoustics, I would probably put the meter on a soft blanket on the =
floor
beneath the midpoint of the "strip" of soundboard immediately under =
the
string, with the mic pointed straight up and the piano lid =
closed.
That's probably as reproduceable as you're going to get.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>For those who aren't knowledgeable in =
electronics, don't worry. This isn't neary as comlicated as it
sounds. It's a very easy project for some electronics =
technician.
Look in the following departments: physics, any engineering, =
neurobiology,
psychology, RTF, possibly even music (???).</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Peace,</FONT></DIV>
<DIV><FONT face=Arial =
size=2>Sarah</FONT></DIV></BLOCKQUOTE></BODY></HTML>