Operation Manual

SUBTRACTOR SYNTHESIZER
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A seasoned synth programmer using Subtractor for the first time may wonder why the
Subtractor oscillators (seemingly) cannot provide the commonly used pulse waveform
and the associated pulse width modulation (PWM). Or oscillator sync, another com-
mon feature in analog synthesizers. The simple answer is that Subtractor can easily
create pulse waveforms (with PWM) and oscillator sync-sounds, and a lot more be-
sides, partly by the use of phase offset modulation.
Each oscillator has it's own Phase knob and a selector button. The Phase knob is
used to set the amount of phase offset, and the selector switches between three
modes:
•Waveform multiplication (x)
•Waveform subtraction (–)
• No phase offset modulation (o).
When phase offset modulation is activated, the oscillator creates a second waveform
of the same shape and offsets it by the amount set with the Phase knob. Depending
on the selected mode, Subtractor then either subtracts or multiplies the two wave-
forms with each other. The resulting waveforms can be seen in the illustration below.
• In example 1, we see two sawtooth waves with a slight offset.
• Example 2 shows that subtracting one slightly offset sawtooth wave from the
other, produces a pulse wave. If you modulate the Phase offset parameter (with for
example an LFO), the result will be pulse width modulation (PWM).
• Example 3 shows the resulting waveform when multiplying the offset waves with
each other. As you can see (and hear if you try it), multiplying waveforms can pro-
duce very dramatic and sometimes unexpected results.
Using phase offset modulation can create very rich and varied timbres, especially
when used along with LFO or Envelopes to modulate the phase offset.
✪ To get a “feel” for this concept, you could study Patches that use phase
offset modulation, and maybe tweak some of the Phase Offset parame-
ters to find out what happens. Try “SyncedUp” in the Polysynth category
in the Factory Soundbank for an example of osc sync or “Sweeping
Strings” (in the Pads category) for an example of PWM.
! Note that if you activate waveform subtraction with a Phase offset set to
“0” for an oscillator, the second waveform will cancel out the original
waveform completely, and the oscillator output will be silent. If you set
the Phase Offset knob to any other value than zero, the sound returns.
Frequency Modulation (FM)
In synthesizer-speak, Frequency Modulation, or FM, is when the frequency of one os-
cillator (called the “carrier”) is modulated by the frequency of another oscillator (called
the “modulator”). Using FM can produce a wide range of harmonic and non harmonic
sounds. In Subtractor, Osc 1 is the carrier and Osc 2 the modulator. To try out some
of the effects FM can produce, proceed as follows:
1. Select an Init Patch by selecting “Initialize Patch” from the Edit menu.
2. Activate Osc 2.
As you need both a carrier and a modulator to produce FM, turning the FM knob
will not produce any effect unless you first activate Osc 2. For classic FM sounds,
use sine wave on oscillator 1 and triangle wave on oscillator 2.
3. Use the FM knob to set the FM amount to a value of about 50.
As you can hear, the timbre changes, but the effect isn’t very pronounced yet.
4. Turn the Osc Mix knob fully to the left, so that only the sound of Osc 1 is
heard.
The modulator (Osc 2) still affects Osc 1, even though the Osc 2 output is muted.
5. Now, hold down a note on your MIDI keyboard and tune Osc 2 a fifth up from
the original pitch by setting the Osc 2 frequency “Semi” parameter to a value
of 7.
As you can hear, for each semitone step you vary the Osc 2 frequency, the timbre
changes dramatically. Setting Osc 2 frequency to certain musical intervals (i.e.
fourth, fifth or octave semitone steps) produces harmonic, rich timbres, almost like
tube distortion. Setting Osc 2 to non-musical intervals usually results in complex,
enharmonic timbres.
1. The two offset
waveforms:
1. The two offset
waveforms:
2. The result of
subtraction:
3. The result of
multiplication:
Ampl.
Ampl.
Ampl.
t.
t.
t.