Moog murf function description

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MF105 - Multiple Resonance Filter (MuRF)
Performance Specification
March 10, 2004 Version

GENERAL

The MF105 Multiple Resonance Filter is an analog audio signal processor with one audio
input and two audio outs. It includes a microprocessor section to read the panel controls
and switches, read the pedal/ control jacks, generate patterns, produce control signals
for the analog circuitry, and drive the indicator LEDs.

The audio signal chain consists of the following sections:

. An input amplifier,

0 Eight resonant filters, each of which is followed by a dedicated VCA,
I A VCA for the direct, unfiltered signal,

0 Two output amplifiers, and

I The usual on/ bypass switching

The outputs of filters 1, 3, 5, and 7 go to the LEFT / MONO audio output, while the
outputs of filters 2, 4, 6 and 8 go to the RIGHT audio output.

Each of the filter VCAs has a separate control input to which an envelope control voltage
is applied. In addition, all of the filter VCAs have a common control input for setting the
overall gain. The direct VCA has a separate control input for controlling its overall gain.

All of the filters have a common control input for shifting their resonant frequencies.
This control signal is a high frequency rectangular wave, the duty cycle of which
determines the amount of frequency shift.

Analog control signal generation and processing consists of the following functions:

I A high frequency oscillator, a variable-threshold comparator, and a driver, for
generating the frequency shifting control signal,

. A level-shifting amplifier for the filter overall gain control signal,

I A level-shifting amplifier for the direct overall gain control signal, and

I A voltage-to-current converter for controlling the gain of the audio input amplifier

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The panel controls and switches, control and timing signal jacks, the stomp switch, and
the peak voltage are scanned by a C8051F005 microprocessor. The microprocessor and
the associated digital circuitry generate the following signals in response to the settings
of the panel controls and the signals applied to the jacks:

. A separate envelope control voltage for each of the filter VCAs,

0 Control voltage for the filter VCA overall gain,

0 Control voltage for the direct overall gain,

0 Control voltage for the gain of the audio input amplifier,

. Control voltage for determining the duty cycle of the frequency shift control signal,

. Switch signal for the on/ bypass function, and

0 Switch signals for the OVERLOAD, PATTERN RATE, and ON / BYPASS indicator
LEDs.

The eight envelopes are produced sequentially, in a pattern that is determined by the
PATTERN selector switch, and at a rate that is determined by the RATE rotary control.

The ENVELOPE rotary control changes the times of the envelope segments. All eight
envelopes are the same shape.

The MIX rotary control determines the relative amounts of filtered and direct audio
signals that appear at the outputs.

The DRIVE rotary control determines the gain of the input amplifier.

The OUTPUT rotary control changes the gains of both the filter VCAs and the direct
VCA.

The function of the two-position panel switch currently labeled BANK has not yet been
fully determined. It will probably be used to enable/ defeat the LFO component of the
frequency shift control signal.

The control and timing jacks perform the following functions:

The RATE, ENVELOPE, and MIX jack signals perform the same function as the RATE,
ENVELOPE, and MIX panel controls.

The LFO jack signal changes the rate of the microprocessor-generated sine wave that is
used for the frequency shift function.

The SWEEP jack signal is combined with the microprocessor-generated sine wave in a
marmer that will be described below.

The TAP jack, when used, disables the microprocessor-generated pattern rate. In its
place, it substitutes the time between the last two transitions to LO at the TAP jack input.