Syntheogen Guide

Subtractive Synthesis

Updated March 28, 2014

Subtractive synthesis is the technique used by classic synthesizers of the seventies, and is still one of the most popular sounds today. Generally, this approach takes harmonically-rich sounds like square or sawtooth waves and 'subtracts' frequencies from them with filters. Syntheogen emulates this process digitally with its subtractive synth.

To use subtractive synthesis, open the TRACK SYNTH dialog and set SYNTH to Subtractive. The following controls will appear:

TRACK SYNTH dialog with subtractive synthesizer

OSC 1

These controls configure the first of the patch's two oscillators:

(oscillator type)	Sets the waveform produced by the first oscillator to sine, square, triangle, or sawtooth.
SEMIS	Sets the number of semitones by which the pitch produced by the oscillator should vary from the notes specified in the pattern.
CENTS	Sets the number of cents by which the pitch produced by the oscillator should vary from the notes specified in the pattern. A cent is one percent of a semitone.
LEVEL	Sets the oscillator's output level.

OSC 2

These controls configure the second of the patch's two oscillators, and they work just as the OSC 1 controls do. The second oscillator's level is not needed when that oscillator is set to frequency-modulate the first, so it does not appear when MIX is set to FM.

MIX

This control determines how the output of the oscillators is combined:

Add	The signals are 'mixed' in the conventional sense, by adding them. When the mix is set to Add, the STEREO knob appears. This control sets the amount of stereo separation between the signals, with zero producing a single mono signal, and 100 panning them hard left and right.
AM	The second oscillator is used to amplitude-modulate the first. When the mix is set to AM, OSC 2 LEVEL serves as the AM modulation index.
FM	The second oscillator is used to frequency-modulate the first. When the mix is set to FM, the INDEX knob appears. This control sets the FM modulation index.

NOISE

These controls configure the noise generator:

TEXTURE	Sets the color of noise added to the signal, with higher values producing darker noise with less high-frequency energy.
LEVEL	Sets the amount of noise added to the signal.

FILTER

These controls configure the envelope filter:

(filter type)	Sets the filter type to Low-pass, Band-pass, High-pass, or None.
FREQ	Sets the filter cutoff or center frequency, in Hertz.
TRACK	Sets the key tracking ratio, which determines the amount by which the filter cutoff varies as notes in the pattern vary.
WIDTH	Sets the range over which the filter transitions from its pass band to its stop band, this varying inversely with the filter's slope or quality factor. Low values produce sharp, distinctive resonance peaks and eventually cause the filter to oscillate. This produces interesting effects, but it can also create extremely loud sounds! Be careful when setting this value.
INVERT ENV	Inverts the filter envelope.
ATTACK	Sets the filter envelope attack time, in seconds.
DECAY	Sets the filter envelope decay time, in seconds.
SUSTAIN	Sets the filter envelope sustain level, in percent.
RELEASE	Sets the filter envelope release time, in seconds.

Filtering is a resource-intensive effect, and filtering at the patch level requires that multiple filter instances be maintained when several notes sound at once. This is unavoidable if the filter must respond to an envelope, but when that is not needed, you should disable the synthesis filter and add an effect filter instead.

LEVEL

These controls configure the level envelope:

ATTACK	Sets the level envelope attack time, in seconds.
DECAY	Sets the level envelope decay time, in seconds.
SUSTAIN	Sets the level envelope sustain level, in percent.
RELEASE	Sets the level envelope release time, in seconds.

LFO 1

These controls configure the first of the patch's two LFOs:

(LFO targets)	Sets the parameters to be modified by the LFO. Unlike many synthesizers, Syntheogen allows a single LFO to have multiple targets; tap any parameter once to select it, then tap again to deselect it. The following parameters can be targeted by either LFO: Osc 1 pitch, Osc 2 pitch, Osc balance, AM index, FM index, Filter freq, Filter width, Pan, and Level.
PHASE	Sets the starting phase of the LFO waveform, in degrees. This determines the point within a periodic waveform at which the modulation starts; it can be used to produce a sine wave that falls at the beginning of the loop (instead of rising), or a square wave that starts at the bottom of its range (instead of the top).
LENGTH	Sets the length, in beats, of one LFO cycle. If a random waveform is selected, this instead determines the time between each check for a new value. Tap the edit box and use the slash key to enter a fractional value.
DEPTH	Sets the intensity of the LFO's effect on the targeted parameters.
(LFO shape)	Sets the LFO waveform shape. The usual periodic waveforms are offered — Sine, Triangle, Square, Saw, and Reverse saw — along with four random shapes: Random peak transitions linearly between random values, producing an irregular series of triangular peaks; Random hold transitions very quickly between random values, and holds each for LENGTH beats, producing an irregular series of square steps; Random pulse outputs the lowest value in the modulation range, with occasional rectangular pulses of random height; Random step produces a series of square steps that increase or decrease one increment at a time, with random direction changes.
CHANCE	If a random waveform is selected, this determines the percent chance at each step that a new value will be chosen, or the chance that the sequence will change direction.
STEPS	If a random waveform is selected, this determines the number of steps into which the modulation range is divided. If STEPS is step to 2, only the highest and lowest values will be chosen. If an oscillator pitch is targeted, setting DEPTH to 100 and STEPS to 25 will produce values from the chromatic scale.

LFO 2

These controls configure the second of the patch's two LFOs; in all other respects, they match the controls in the LFO 1 section.

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