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Synthesis with the MOD-7: a guided tour Overview
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Synthesis with the MOD-7: a guided tour
Overview
The tutorials below provide a guided tour of the MOD-7’s
synthesis capabilities. They start with a little background
information, and then dive right into step-by-step
instructions for creating simple sounds from scratch, using
all of the MOD-7’s major features.
Please read each section in order, since the later ones rely on
what you’ve done earlier.
VPM and FM Synthesis
Variable Phase Modulation (VPM) synthesis refers to Korg’s
patented contributions to Frequency Modulation (FM)
synthesis.
Carrier-modulator pairs
In its most basic form, these synthesis methods use a pair of
oscillators: a modulator and a carrier. Only the carrier is
connected to the audio output. The modulator is not heard
directly; instead, its output modulates the frequency (or
phase) of the carrier.
This modulation creates changes in timbre. The relative
frequencies (or “ratios”) of the two oscillators determines
which overtones are produced, and the level of the
modulator controls the loudness of those overtones.
In general, whole-number ratios produce harmonically
related overtones, fine deviations from whole-number ratios
produce similar overtones with chorusing, and more
complex ratios produce wild, clangorous overtones.
Greater complexity
Most modern VPM and FM synths allow more than simple
oscillator pairs. For instance, a modulator might itself be
modulated, to create a more complex timbre; two modulators
might have separate paths into a single carrier; a single
modulator might be sent to two or more carriers; and so on.
A carrier might both be heard directly, and also act as a
modulator on another oscillator. Feedback paths may let a
carrier modulate itself.
In the MOD-7, these routings are created on the Patch Panel,
by selecting an algorithm, creating patch cables, or a
combination of the two.
The more complex the routing and frequency relationships,
the more difficult it can be for even experienced sound
designers to predict the results. As legend has it, the main
breakthrough for FM itself came from a mistake, when FM
pioneer John Chowning programmed an LFO with a
frequency 100 times faster than he’d intended. When
working with the MOD-7, take a cue from his example: keep
experimenting, and leave your ears open for “happy
accidents.”
VPM, PCM, Waveshaping, and Ring Mod
The MOD-7 combines VPM with PCM sample playback,
waveshaping, ring modulation, and dual multimode resonant
filters, It’s a powerful digital synthesis toolkit, and it can be
approached from many different angles, as discussed in the
tutorials below.
Aliasing
Multiplying one audio-rate signal with another generally
causes aliasing, and VPM is no exception. Higher modulator
levels can produce aliasing artifacts, from low-level grunge
to phantom pitches to, at the extremes, loud white noise.
This becomes more of an issue with higher frequencies, such
as when playing in the top octaves of the keyboard.
Sometimes, these artifacts may be useful as part of the
overall timbre; other times, they may be unwelcome guests.
The most valuable tool to mitigate aliasing is Key Tracking,
which lets you reduce the modulator levels at higher
frequencies, while keeping them stronger at lower
frequencies. The MOD-7 includes dedicated multi-point key
tracking for each VPM Oscillator.
Creating an initialized MOD-7 Program
For the tutorials below, we’ll need to start with an initialized
MOD-7 Program. To do this:
1. In PROGRAM mode, select factory Program INT-C
050, “Cat On aMoJo V2.”
2. Go to the PROGRAM > Basic/X-Y/Controllers–
Program Basic page.
3. Change the EXi1 Instrument Type from CX-3
Tonewheel Organ to MOD-7 Waveshaping VPM
Synthesizer.
If you’ve already been working with the MOD-7, and want
to return to an initialized state:
1. Select the EXi1 Instrument Type parameter.
2. Use the - button to change it to PolysixEX.
3. Use the + button to toggle it back to MOD-7.