10
9 Waves make up a wave table
Ring Modulation
A Ring Modulator is a sound generator that takes signals from two of the MiniNova’s
oscillators and effectively “multiplies” them together. The MiniNova has 2 Ring Modulators,
one takes Osc 1 and Osc 3 as inputs, and the other takes Osc 2 and Osc 3. The resulting
output depends on the various frequencies and harmonic content present in each of the
two oscillator signals, and will consist of a series of sum and difference frequencies as well
as the frequencies present in the original signals.
The Mixer
To extend the range of sounds that may be produced, typical analogue synthesizers have
more than one Oscillator. By using multiple Oscillators to create a sound, it is possible
to achieve very interesting harmonic mixes. It is also possible to slightly detune individual
Oscillators against each other, which creates a very warm, ‘fat’ sound. The MiniNova’s
Mixer allows mixing of three independent Oscillators, a separate Noise Oscillator and two
Ring Modulator sources.
The Filter
The MiniNova is a subtractive music synthesizer. Subtractive implies that part of the sound
is subtracted somewhere in the synthesis process.
The Oscillators provide the raw waveforms with plenty of harmonic content and the Filter
section subtracts some of the harmonics in a controlled manner.
14 types of Filter are available on the MiniNova, though these are varieties of three basic
filter types: Low Pass, Band Pass and High Pass. The type of Filter most commonly
found on synthesizers is the Low Pass type. With a Low Pass Filter, a cut-off point
(or cut-off frequency) is chosen and any frequencies below the point are passed, and
frequencies above are filtered out. The setting of the Filter Frequency parameter dictates
the point below which frequencies are removed. This process of removing harmonics
from the waveforms has the effect of changing the sound’s character or timbre. When the
Frequency parameter is at maximum, the filter is completely “open” and no frequencies are
removed from the raw Oscillator waveforms.
In practice, there is a gradual (rather than a sudden) reduction in the volume of the
harmonics above the cut-off point of a Low Pass Filter. How rapidly these harmonics
reduce in volume as frequency increases above the cut-off point is determined by the
Filter’s slope. The slope is measured in ‘volume units per octave’. Since Volume is
measured in decibels, this slope is usually quoted as so many decibels per octave
(dB/oct). Typical values are 12 dB/oct and 24 dB/oct. The higher the number, the greater
the rejection of harmonics above the cut-off point, and the more pronounced the filtering effect.
A further important parameter of the Filter is its Resonance. Frequencies at the cut-off point
may be increased in volume by the Filter Resonance control. This is useful for emphasizing
certain harmonics of the sound.
As Resonance is increased, a whistling-like quality will be introduced to the sound passing
through the filter. When set to very high levels, Resonance actually causes the filter to
self-oscillate whenever a signal is being passed through it. The resulting whistling tone
being produced is actually a pure sine wave, the pitch of which depends on the setting of
the Frequency control (the filter’s cut-off point). This resonance-produced sine wave can
actually be used for some sounds as an additional sound source if wished.
The diagram below shows the response of a typical low pass filter. Frequencies above the
cut-off point are reduced in volume.
Volume
In addition to the traditional Low Pass Filter type, there are also High Pass and Band Pass
types. The type of Filter used is selected with the Filter Type parameter.
A High Pass Filter is similar to a Low Pass Filter, but works in the “opposite sense”, so that
frequencies below the cut-off point are removed. Frequencies above the cut-off point are
passed. When the Filter Frequency parameter is set to zero, the filter is completely open
and no frequencies are removed from the raw Oscillator waveforms.
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