Understanding the MMG
The MMG is no more complicated than other synthesizer filters, however it does have some features that
are less typical.
The INPUT Stage: There are two inputs which allows for mixing two signals at the input of the MMG. One
input is marked AC IN and the other is marked DC IN. These names reflect how the signal is coupled into
the circuit. AC IN is AC coupled, which is the standard way to inject an audio signal into a filter. AC coupling
into a filter conserves bandwidth and prevents asymmetrical clipping of the signal. The DC IN is direct
coupled into the circuit. This is not a common way to couple a signal into an audio filter since it allows for
loss of bandwidth and asymmetrical clipping. We have included the DC IN because it allows for processing
control signals with the MMG as well as programming asymmetrical clipping. Patch an LFO to DC IN and
your audio signal to the AC IN. Set the AC IN Attenuator to taste. Set the MODE to LP and observe the
behavior of the circuit as you turn up the FREQ and Q panel controls.
The MMG Q Factor circuit is highly dependent upon the input signal levels. For this reason we have included
the AC IN Drive control and Over Load indication LED. When this LED lights, you have exceeded the ideal
input signal levels for operating the MMG. Do not fear though, you cannot damage anything by over loading
the circuit! The ideals were designed to be exceeded! When over loaded, there are some distortions that
occur and the strength of the resonance is lessened; it might be just the sound you are seeking.
The MODE control There are two modes of operation on the MMG, Low Pass and High Pass. Unlike the
original QMMG, these modes are not switched, but rather they are swept. As you turn the MODE panel
control you are changing the circuit topology from LP to HP!
The MODE CV IN has a Bi-Polar Attenuator associated with it. This allows for adding or subtracting a control
voltage from the MODE Panel control setting. Keep in mind there is a normalization between the
FREQuency control signal and the MODE CV input that allows for a quasi-band-pass behavior to be
programmed (with nothing patched to MODE CV IN, set MODE to LP, and MODE CV Attenuator to full CW).
To eliminate this behavior, set the MODE CV attenuator to 50% or patch a dummy cable into the MODE CV
INput.
The Cut-Off FREQuency control This section of the MMG is not unlike most analog Voltage Controlled
Filters. With MODE set to LP, increasing the cut-off frequency is like opening the up the sound, making it
brighter. With MODE set to HP increasing the Cut-Off frequency is like shaving away the sound, making it
thinner.
The MMG has two CV inputs for Cut-off FREQuency control. FREQ 1 has a Bi-Polar Attenuator associated
with it. This allows for adding or subtracting a control voltage from the FREQ Panel control setting. FREQ 2
has no attenuator, and is a unity gain control signal input. This means it will be directly applied to the Cut-off
FREQuency setting. FREQ 2 is a good input to use when you have a control signal that does not require
further processing, such a programmed sequence or a signal that has already been processed by a channel
of MATHS.
(12 pages)
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