Re: tone wheel or electronics ?

[bpb@bpbsn.cca.rockwell.com (Brad Baker)]

Regarding Re: tone wheel or electronics ?; Don Tillman <don@till.com> adds:

  > Date: Tue, 9 May 1995 14:34:37 -0600 (MDT) From: John Fisher
  > <John.Fisher@m.cc.utah.edu>

    >> On the down side of things, tone wheel generation does not
    >> produce an even tempered scale.

  > Huh?  Whaddaya mean?  Sure it's even tempered.

well, i don't think it's _exactly_ even tempered since its done using
integer math (gears, tonewheel bumps). i wonder how close it is? i'd
be interested in knowing the exact pitches produced. it would make a
nice boring project for someone having a disassembled tone
generator. all this idle person would really have to do is count the
teeth on the driven and driving gears of the 12 main shafts in the
tone generator. hey al!  hey dave!  you guys aren't doing anything are
ya?

    >> THE NEAT THING SOUND WISE is that every note is absolutly phase
    >> locked - ZERO beat frequencys -VERY important and even more so
    >> when played through a leslie on fast speed.
                             ^^^^^^^^^^^^^^^^^^^^
it does seem to be more noticable/objectionable in this case.

  > Huh again?  How do you mean phase locked?  There's no locking
  > mechanism happening and the 1.5 and 3rd harmonics will be beating
  > with the fundamental.  Especially if you crank it a little.

i think he's talking about the drawbar harmonics for a particular
fundamental being tone generator derived as opposed to being derived
from the natural harmonics of that fundamental. since the whole thing
is physically geared together it's in a sense "phase-locked".

regarding the beating of fundamental with harmonics, one of the
interesting peculiarities of hammond's pitch set causes it's harmonic
beating characteristic to be opposite, in a certain sense, to the
beating characteristic of non v-3 organ simulators. since they have
natural drawbar harmonics, they produce that beat that john hears and
we've discussed here before - lets' call it... natural harmonic
beating (nhb) - whenever a fundamental is played that corresponds to
drawbar harmonic of some lower fundamental. the tone generator derived
pitches don't produce nhb, at least not until, as you say, you "crank
it a little".  when you crank it the distortion products produced are
natural harmonics and now you just might hear nhb occuring between the
distortion products of the fundamental and that fundamental's drawbar
harmonic. the natural harmonic organ sim, otoh, won't do this cuz the
frequencies of the distortion products of a particular fundamental are
the same as the frequencies of that fundamental's drawbar harmonics.

brad baker
bpb@mlb.cca.rockwell.com