Reason’s Subtractor is a virtual synthesizer which models classical analog hardware, combining chains of several types synthesis into one device. It features wavetable synthesis (the actual sound generators, the waveforms), subtractive synthesis, and several levels of modulation (pitch, amplitude, filter frequency, phase, etc). Understanding the signal path within this network of sound producing and sound modifying modules will help you grasp just what the Subtractor can do.
First, the two available oscillators (VCO, Voltage Controlled Oscillator) constitute the sound source. There are classical waveforms such as the sine wave, triangle wav, square wave, sawtooth wave, etc., but Reason has it’s own family of waveforms as well. A complete description of each available waveform along with playable soundfiles can be found here.
Second, the new waveform passes into the filter-section (VCF, Voltage Controlled Filter) where various filter types (high-pass, low-pass, band-pass, notch) alter the spectrum of the original oscillator. This is the “subtractive” portion of the Subtractor and where a lot of the magic happens. Filters can give life to otherwise static timbres.
The third step is allows you to control the waveform’s amplitude envelope. Here the standard ADSR envelope is used.
There are four parts to the envelope, one for each of A-D-S-R:
Attack – Decay – Sustain – Release
–Attack controls the onset of the note, how fast a signal goes from zero to it’s maximum level.
–Decay determines the amount of time it takes for a signal to “decay” to the Sustain level following the attack.
–Sustain is important for the level which is held until a note ends.
–Release, finally, how fast the envelope fades to zero after the key or MIDI note is released.
Subtractor’s section four similarly allows you to apply an ADSR envelope to the modulator and the filter. These control the onset and release of the modulation and filter, respectively. Think of it as an automated, time-varying control of the Modulation and Filter knobs.
Finally in stage five, the signal is modulated by an LFO (Low Frequency Oscillator). This LFO can modulate any one of several parameters of the sound. Toggling through the various modes you will hear how this impacts the timbre. LFO’s are slow-moving waveforms which are used to modulate some aspect of the original “carrier” signal, creating motion within the sound, adding richness and life to the sound. Notice that LFO 2 has something that LFO 1 does not: a delay. This allows the modulator to be activated at some time later than the initial attack, as is often the case with singers and other physical instruments.