MOTM

Use the linear FM on your VCOs for natural-sounding vibrato. You don't need
a special VCO that has an 'anti-exponential' waveshape or anything. Did I
understand the question correctly?

You certainly can chain multiple envelope generators, or mix several
simultaneous contours. I'm not sure exactly what kind of envelope you're
describing there. It may be a "Yamaha DX/TX" type envelope with
'sustain-level/rate/sustain-level/rate...' This type of EG has been
discussed here as a possible future module, but I don't think there are any
immediate plans for one. The classic Ussachevsky "ADSR" is the simplest way
to capture the main points of many natural acoustic sounds, and is a 'bang
for the control buck' compromise that works pretty well. But I find that you
can never have enough envelope generators.

Inverting a CV just makes a negative voltage positive or a positive one
negative. Inverting an AC signal does the same thing, which you can think of
as a 180-degree phase shift, a mirror image across zero-crossing (ground).
Some MOTM modules feature reversible attenuating inputs, and I believe the
soon to be released Mixer will have inverting capabilities. If you want to
talk about continuously specifying phase shift, you're starting to talk
about a delay line of some sort. You can't just shift the phase of an
incoming signal by some fixed amount, since phase is related to pitch and
time.

Mixing and summing are the same thing. "Mixing" implies having continuous
control over the levels being summed, whereas summing 'implies' a static
relationship. But really they are the same thing. Which you use is a matter
of preference or context.

Certainly you can use the [forthcoming] envelope follower to do what you
describe. The term "Formant Modulation" is a bit odd though. Technically,
anything you do to the frequency spectrum, amplitude-wise, is modulating the
formant. Any type of filter alters the formant, which is the 'spectral
envelope/contour' of a sound. Graphic equalizers, lowpass filters, phase
shifters (comb filters)... all devices of this nature modify the formant.

Acting on one "half" of an AC waveform, with respect to zero-crossing
(ground) is called "rectification." If you are just removing the top or
bottom half, it is called "Half-Wave Rectification," and if you flip one
half into the space on the other side, like a mirror, it is called
"Full-Wave Rectification." In theory you can do this with four diodes in a
classic "bridge" configuration, but in practice when dealing with audio, you
really want to use op-amps, etc. The diode bridge full-wave rectifier is
commonly used in power supplies to convert AC to DC by flipping the negative
phase of the power signal up to the positive side. Then you filter out the
ripple with a couple of caps and you have a DC voltage. (This is all quickie
black-box talk you understand.) Envelope Following is a similar FWR process.

The MOTM "vibrato" is filtered white noise. It's not a replacement for an
LFO, it is a unique method of getting an LFO-like signal with slight random
variations by using a very peaky bandpass filer around 7 Hz (I think...
don't have the info in front of me). You could theoretically change the
"rate" by changing the filter's center frequency, but this isn't a feature
of the module. I don't really know how useful it would be to do that. You
could use pink noise to modulate the frequency of the VC LFO if you need
that effect.

Hope some of this helps.



 -----Original Message-----
From: 	mark scetta [mailto:n0nspaz@...] 
Sent:	Thursday, 06 April, 2000 3:39 PM
To:	motm@onelist.com
Subject:	[motm] q&a 

so who's up for a little quiz? :)

i've been reading thomas wells' 'the technique of electronic music' and boy 
do i have some questions. in no particular order:


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?

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

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?

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

wells describes formant modulation as modulating the cutoff freq of a 
carrier with the amplitude of a modulating signal.  how does this work in 
real life?? will i be able to send a carrier signal into a motm440 and 
control its cutoff with a modulating signal sent through an envelope
follower?

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

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

regards!
mark in providence