• Subtractive analog synthesizer
• 37-key slimkey keyboard
• Polyphonic aftertouch
• 4 voices (incl. unison & mono)
• 2 oscillators (all waveforms can be activated simultaneously)
• Oscillator B with 2 low modes
• hardsync
• Noise generator
• mixer
• 24dB Lowpass filter
• 2 ADSR envelopes
• 1 LFO with sync
• Arpeggiator
  
• Step sequencer
• Modulation bus
• Assignment for aftertouch
• Handwheels for Pitchbend & modulation
• Pedal input for expression or footswitch
• MIDI In / Out / Thru
• USB MIDI
• Headphone output
• Main Out (mono)
  

Classic modulation sources and the Pro-One modulation bus

The FOURM has four primary modulation sources. The two crisp ADSR envelopes are permanently assigned to the filter and VCA. The synchronizable LFO with four simultaneously activatable waveforms is assigned in the modulation bus. The (polyphonic) aftertouch section can modulate up to three destinations simultaneously, which are divided into the groups frequency OSC A/B, cutoff/amp, LFO frequency/amount.
The modulations are assigned on the left of the control panel. This is the modernized form of the modulation bus from the SCI Pro-One from 1981. The filter envelope, oscillator B and the LFO, each with its own attenuator, are available in parallel as sources. These are assigned to the targets Frequency Oscillator A+B, Pulse Width Oscillator A+B, Cutoff, Amp, LFO Frequency and LFO Amount via buttons. The color coding provides information about the modulation links. Red or blue means from one source to one or more destinations; purple has 2-3 modulation sources.
Used carefully, wild oscillator drifts, sync sounds, sirens, FM for filters and/or oscillator A as well as pulse width modulation are possible. Turn it all up at once and it gets really wild!