Allen Organs and Stretch

[Robert Scott]

Del Gittinger wrote:

>Contrary to popular belief, ANY electronic device with an oscillator with a
>capacitor in it, even digital instruments, will drift in frequency over
>time.  Therefore, even an Allen digital organ will not necessarily stay at
>A=440 hz forever.  A computer will tolerate minor changes in the actual
>frequency of the oscillator but the same change will mean a difference of
>several cents pitch for audio frequencies.

   My Gittinger's observation is accurate as applied to oscillators based
on capacitors (usually in combination with coils).  Although quartz crystal
oscillators are much more stable, they are not easily adapted to being the
master oscillator in an electronic organ.  The same property that makes
them stable also makes them difficult to adjust over a wide range.  A typical
quartz crystal oscillator can only be adjusted about 0.1 cents.  So if an
electronic organ were made using a quartz crystal oscillator, it could be
designed to stay put at A-440 for years, but you could not tune it to A-444.
Apparently the designers of the Allen organ decided that flexibily in
offset tuning was worth the degraded stability that comes with non-quartz
oscillators.

  Mr. Gittinger's observation about computers, while true, is also
misleading.  It might lead one to think that computers generally use
such unstable oscillators.  The fact is that almost all modern computers
use quartz crystal oscillators that are very stable.  If they did not, then
certain time-related functions, like the system time and date, would
drift unacceptably.

   -Bob Scott
   -Ann Arbor, Michigan