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Subject: Re: [motm] q&a

From: jwbarlow@...
Date: 2000-04-06

In a message dated 4/6/2000 1:07:58 PM, n0nspaz@... writes:

>he talks about exponential vs. linear VCOs: expo. being for audio signals,
>lin. to be used for frequency modulation of other signals (as CVs). are
>there any plans for linear MOTM VCOs?

The MOTM 300s do have linear FM (there's even a switch EXP/LIN for the FM1
input). There was talk about a Through Zero Linear FM VCO, I'd like to hear
more about this. Through zero FM is supposed to produce even more rich
timbres when used for audio FM.

>how would one realize the following envelope: ADS DS DS ... R ? by
>chaining ADSRs somehow?

I'm going to think about this a bit more, it looks like it would require some
additional modules (maybe just comparators).

>inverters: will a future MOTM inverter most likely change a signal's phase
>180 degrees, or might it be adjustable over a range? and will it do the
>same for CVs?

An inverter always changes the phase of a signal 180 degrees, changing phase
by anything other than multiples of 180 (like 360) requires a filter, phaser
or delay (something else?). Many of the MOTM inputs already allow inversion.

>would someone tell me the (electrical) difference between mixing and
>summing signals?

Generally, these are synonymous. However, you can mix with a difference
amplifier, which means the two (most simple example) are subtracted from one
another. This same effect can be achieved by inverting one input of the
mixer. This type of mixing would be most useful for control voltages, or from
subtracting out harmonics from a single VCO (I've been doing this a lot

>wells describes formant modulation as modulating the cutoff freq of a
>carrier with the amplitude of a modulating signal. how does this work
>real life??

Real life example:
1) one MOTM 300 output to MOTM 420 (or 440) input
2) second MOTM 300 output to MOTM 420 (or 440) FM 1 input
3) now change the FM 1 knob with your hand. You are now changing the
amplitude of the modulation. Remember, at the 12 o'clock position it's at
zero amplitude.

To do this in a more "modular way" you'd need to insert a VCA in between the
second MOTM 300 and the FM1 input.

will i be able to send a carrier signal into a motm440 and
>control its cutoff with a modulating signal sent through an envelope
>how to 'remove' one side of an AC waveform and be left with only its neg.
>DC component or its positive? (am i using proper terminology?)

I'm not sure I understand this. You could use an envelope follower to follow
the envelope (maybe that's obvious), and use the EV output to control a VCA
which gated the modulation of a filter.

As far as the AC goes, I think you're asking about rectification. There's two
kinds, full wave, and half wave. This has it's uses in timbre modulation.

>i know we've been over this before, but why is it not possible to control
>the MOTM100's vibrato rate with a pot?

It probably is, it would just cost more.

>i'm all intrigued with frequency and amplitude modulation now. i look
>forward to having the modules to experiment with sideband suppression and

Don't we all!

Still thinking about the ADSR question.