From bruce@ashbysolutions.com Tue Aug 21 18:36:25 2001
Subject:Re: Foldback (was: Nord Electro)

All,

Regarding foldback: There are two areas of foldback, and they probably
should be discussed separately:

Lower Foldback --

This was caused by Hammond's addition of "special" tone-wheels for the bass
pedals in the late 40's/early 50's, around the time that the BC became the
BV, I think. The lowest octave of a B-3's wheels do not produce the
classic sine-like wave; rather, they make a wave that is more complex in
timbre. It was decided -- and rightly so, IMHO -- that these tones did not
work well on the main keyboard, and so the last octave of 16' pitches was
folded back.

The V3 give the user a choice between low foldback or none, and I used each
kind for about a year and a half. Both had their strong points --
FB: smoother tone and less breakup in the amp; No FB: deeper bass,
especially on "thunder" glisses -- and weak sides -- FB: less pronounced
bass, especially on held octave notes; No FB: the frequency of the tones
goes lower than many amps can follow. I never really found a clear winner,
and tended to change the setting every few months.

Upper Foldback --

This is a different animal. One of the reasons that the Hammond Organ
sounds so sweet is that it is essentially a midrange instrument. The
foldback prevents any harmonics above 5-6kHz, which tend to cause aural
fatigue or even annoyance. I've owned several clones over the years that
did not provide upper foldback, and I didn't care for the results -- too
shrill for my tastes, especially in the last octave.

It also allows for some musically useful tricks. Try playing a riff or run
in the top octave, and move it down through the organ's range. If you have
a setting like 888000008, the result sounds as if additional voices are
being added throughout the pattern, similar to the effect that classical
composers got by adding additional instruments to a composition, each one
imitating the ones before it.

There's also a practical aspect to foldback, even in modeled
instruments. In order to accurately model a sound, a fairly large number
of samples (10 or more) have to be created at various points in the
waveform. If you don't obey this principal, you end up with digital
"aliasing". (Digital lab instruments ran into this wall years ago.) The
more samples per wave cycle, the better the replication of the original
sound. The problem is: The higher the frequencies go, the more difficult
(read: more expensive) it becomes to reproduce them, while maintaining the
desired sample rate. For every cycle of sound, a modeling CPU has to
execute dozens, if not hundreds, of instructions. By limiting the maximum
frequency of harmonics to around 5-6KHz, rather than say, 10-15kHz, the CPU
can run at half-speed, or double-accuracy, your choice. Either way, it
leads to better sound and lower costs.

Regards,

-BW

--
Bruce Wahler
Design Consultant
Ashby Solutions™
www.ashbysolutions.com
CloneWheel Support Group moderator
978.386.7389 voice
978.964.0547 fax
bruce@ashbysolutions.com