Fw: Electronic Sustain Timer

[Sarah Fox]

Hi Robert,

>  >This isn't nearly as complicated as it sounds.
>
> No, it's much more complicated.  I know because I have done it in TuneLab.
>
> If you look closely at the amplitude variations that occur as a note
> decays, you will see that even if only one string is sounding, there is
> still a beat-like variation due to the precession of the string from up
0and
> down motion to its ultimate elliptical orbit.  Any falseness in the string
> makes matters even worse.

Your point is well taken, but my method actually takes that into account.
(Perhaps I didn't make a big enough point of it in the original post.  I did
talk about it though.)  As both the upper and lower thresholds are
crossed, the beating will cause the timer to switch in and out (or
start/stop
/start/stop or "stutter," if you will).  The final time reading will
be a reflection of the total time spent between the threshold bounds.  If
the beating is the same at the low amplitude (amplified 40 dB) as
it is at higher amplitude, the jittering across the thresholds should have
the same profile, and hence the demarcation of the "start" and "stop" times
will "stutter" the same.  I don't know if I'm describing this clearly.  Am I
making sense?

The circuit I propose is *really* easy and lends itself well to repeat
measurements on many notes without time intensive calculations.  The method
you propose probably also works well.  However, an electronic method of
rectifying and averaging somewhat avoids the problem of the entry and exit
of harmonic components as their vibrational components "rotate" randomly
with respect to the fundamental.  Put another way, the peak profiles can
have weird beating patterns of their own, even when the RMS value of the
waveforms may be the same.  Of course only true RMS averaging would give us
"the" answer, but simple averaging comes close.  Peak detection is the
worst.
I suspect this is a small point, though, and your method should work fine.
Whatever works...

I'll check out Tune Lab.  Thanks!

Peace,
Sarah