Well, I do have one suggestion you may want to consider as an inexpensive
way to get very finite control of generating these harmonics of various
amplitudes. The resulting waves can then be burned into EPROM and used in
the Miniwave. I have actual recently been successful doing this and having
another list member burn the PROM.
Korg made only 2 sampling instruments before they bowed out of that market
and moved toward sample ROMS (i.e. just before the M1) One of those
instruments was the DSS-1. It was a unique instrument that was a 100%
analog synth except the oscillators were digital waveforms. The waveform
source could be from one of three sources: 1= actual sampled sounds, 2 =
draw your own wave form, and 3 = harmonic synthesis. You could select the
fundamental and any of the first 128 harmonics of that frequency. You could
individually specify the level of each harmonic is a resolution of 0 to 255.
each time you added a new harmonic, the DSS-1 would calculate the resulting
wave and create a new composite wave.
Korg did a lot of this to produce single cycle waves for use as oscillator
waves in their synth. For example, they have a "voice wave" and an "organ
wave" The organ wave has the kind of harmonics you would expect to see in
drawbar style organs.
Now, once these waves are created, they can easily be dumped to PC via MIDI
and converted to the 8 bit binary file required for the Miniwave PROMS. I
took all the factory Korg single cycle waves and dumped them to this format
and have them in a PROM (thanks to another listmember). So, one could create
harmonic combinations all day long with the DSS-1 and dump them to PC for
Miniwave PROMs. Of course, once in that format, everything is static. But,
with the ability to sweep waves and banks in the Miniwave, that becomes very
useable.
Working condition DSS-1s sell for about $250 these days. Many of them have
broken disk drives (which you don't need) for this feature and sell for much
less.
So, there is another already invented wheel you could consider.
Larry Hendry
----- Original Message -----
From: paulhaneberg <phaneber@...>
I have also been contemplating trying to build a MOTM style Fourier series
generator. This is a big design project, so I'm asking if anyone has any
ideas to let me know. I'd rather not reinvent the wheel. I do realize I
can do this sort of thing with a lot of MOTM oscillators (as I did on the
ELP thing) but I'd like to find something a little lower in cost than buying
16 MOTM300s ;) And it's not easy to tune a number of 300s precisely enough
to get a good harmonic series even using sync. (I've found it is difficult
to get sync once you get above the 8th harmonic, at least on certain
partials.)
My idea is to take the triangle output of a MOTM300 and frequency multiply
it using a series of rectifiers and amplifiers up to
perhaps 256 times the original frequency. (A rectified triangle wave is a
triangle wave at twice the frequency of the original.)
The resulting waveform would be transformed into a clock signal driving a
series of counters which would count from 0 to 255 then reset. Each counter
would address a sine wave lookup table with a single sine wave divided into
256 increments. Each counter would increment by an amount equal to the
harmonic it was generating. For instance the 3rd harmonic counter would
increment by three on each pulse, the 13th harmonic counter would increment
by 13 each pulse.This would create a series of sine waves albeit digitally
produced which would then be filtered down so that there would be individual
outputs for each harmonic. Presumably the whole thing would be multiplexed
and perhaps implemented within a PIC if it's capable of
going fast enough.