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SUBTRACTOR SYNTHESIZER

104

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 mul-

tiplies the two waveforms 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 produce very dramatic and sometimes unexpected results.

Using phase offset modulation can create very rich and varied timbres, espe-

cially 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 Off-

set parameters 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 si-

lent. 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 oscillator (called the “carrier”) is modulated by the frequency of another os-

cillator (called the “modulator”). Using FM can produce a wide range of har-

monic 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 fol-

lows:

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 in-

tervals (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.

✪ Experiment with different oscillator parameters such as phase off-

set modulation, changing the waveforms etc. and listen to how they

affect the sound of frequency modulation.

Using the Noise Generator as the Modulator source

As explained earlier, the Noise Generator is internally routed to the Osc 2 out-

put. Hence, if you deactivate Osc 2, and activate the Noise Generator while us-

ing FM, the noise will be used to frequency modulate Osc 1.

1. The two offset

waveforms:

1. The two offset

waveforms:

2. The result of

subtraction:

3. The result of

multiplication:

Ampl.

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Propellerhead Reason Spécifications Page 106

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