electro harmonix frequency multiplexer

Harry Bissell harrybissell at prodigy.net
Wed Aug 30 17:42:04 CEST 2000


I'm doing something similar... I convert the square to a triangle... then
half-wave
rectify and AC couple so that the result has a half triangle shape and then the
retrace
of the coupling cap to "restore" the dc level. This gives a sort of square to saw
converter
that isn't very sensitive to a little noise.  Then dynamic LPF with a photocell 2
stage filter.
(cause I could not fit any more circuit on the board).  I'm using it with a low
note priority
string select for playing guitar/bass at the same time.  The overall circuit is
incredibly
complex... but will not octave hop!  The points where octave hopping would
normally occur just cause a phase inversion (shift) that is heard as a tiny
glitch...

Wow I want to see that sine wave unit too....


BTW:  does anyone know why frequency shifters (of the sin-cos or sin^2 type) work

fine for all waves that consist of ODD harmonics only.  Sine will work... so will
triangle,
square... but not any wave with even content.  WIERD! even a tiny amount of even
harmonic kills the doubling right off.

H^) harry

"Goddard, Duncan" wrote:

> >>>It basically converts the frequency to an octave lower,
> > in order to convert guitar into "bass".
> > I saw a scope screenshot, sine in and (almost) sine out.<<<
> >
> every one of these I've seen or used works the same (cheap) way; the input
> is clipped or schmitt-triggered into a square-ish shape and then divided
> down using "logic"...... then the result is lpf'd or waveshaped and mixed
> back with the original. the boss/roland version is the best of a bad lot;
> the modified signal on it's own has a weird timbre that doesn't really work
> in a guitar-context. chords sound awful, obviously.
>
> I came across a device a couple of years ago that was supposed to shift the
> input signal *up* an octave; it was part of a fuzzbox called a "foxtone". my
> task was to copy the interesting bit of this thing and squish it into a big
> muff (oo-er!). it turned out to be a phase-splitter, with one output being
> inverted and added then the new funny shaped waveform (all even harmonics, I
> expect someone will point out) being waveshaped into something resembling a
> sawtooth prior to further distortion. I was astonished to actually hear this
> thing on a guitar instead of just looking at it on a 'scope. it worked very
> well for lead parts but again, not for chords.
>
> d.
>
> (p.s. going home in a minute to play with phattytron)
>
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