4-Voice analog synth with polyphonic aftertouch

Fourm is a compact analog synthesizer that invites you to play, shape, and perform with unprecedented expression. With its legendary Sequential tone, hands-on modulation, and uniquely responsive Tactive™ keybed, Fourm is a creative partner helping to bring your musical ideas to life.

100% Analog

Fourm delivers four genuine voices of Sequential analog sound, built on the legendary Prophet-5 voice architecture—right down to its characteristic envelope response curves. With dual oscillators offering simultaneous wave selection and a classic 4-pole low-pass filter with bass compensation, Fourm captures the warmth and punch that shaped a generation—and takes it to the next level.

2 Analog Oscillators

Fourm’s analog voice path is built around a modern oscillator chip inspired by the design used in the original Prophet-5 Rev 2. It delivers the same rich, musical tone as its vintage predecessor, now enhanced by the benefits of contemporary engineering — improved stability, reliability, and consistency. It’s the perfect foundation for Fourm’s 100% analog sound.

4-Pole Low-Pass Filter

Fourm’s analog 4-pole lowpass filter chip is based on a classic design known for its rich, organic tone and musical resonance. The modern implementation faithfully preserves that sonic character while adding bass compensation. Now you can crank the resonance without sacrificing low-end power — keeping your sound full, bold, and unmistakably analog.

Synthesis

• Two Prophet-5 lineage analog oscillators per voice
• All oscillators have simultaneously selectable waveforms, including the LFO
• Oscillator B supports low frequency modes for use as polyphonic LFO modulation
• Classic Prophet-style Sync
• Variable square wave pulse width per oscillator (PWM)
• 4-Pole resonant lowpass filter drawn from the Prophet-5, revs 1 & 2
• Filter enhanced with bass compensation for thick sounds even with high resonance
• Filter can be driven into self-oscillation with the resonance control 
• Filter Keyboard tracking: quarter, half, full
• Feedback with an aggressive drive circuit for extra edge

• White, pink, and violet Noise types allow for greater sonic variation
• Four-stage (ADSR) filter envelope generator for tone shaping and assignable modulation
• Four-stage (ADSR) Amp envelope generator for volume shaping

• Velocity modulation of envelope amounts for dynamic performance
• One global LFO for creating movement in the sound
• Seven LFO wave shapes: sine, sawtooth, reverse sawtooth, square, S/H (sample and hold), Noise, and DC

• LFO can synchronize to tempo at different step values
• Four LFO wave shapes can be selected simultaneously for complex modulations

Enhancements

• Up to six polyphonic aftertouch destinations selectable simultaneously
• Polyphonic aftertouch destinations: oscillator A frequency, oscillator B frequency, filter cutoff, amplitude, LFO frequency, LFO amount
• Pro-One style top-panel modulation matrix
• Two modulation buses with multiple sources and destinations and the ability to combine both buses at the destination
• Top panel modulation sources: filter env, oscillator B, LFO
• Top panel modulation destinations: oscillator A frequency, oscillator B frequency, pulse width A, pulse width B, filter cutoff, amplitude, LFO frequency, LFO amount

• Polyphonic glide (portamento)

• Unison (monophonic) mode with configurable voice count, from one to all four voices, plus chord memory
• Vintage setting recreates classic synth characteristics by adding voice-to voice variations in component behavior

• Arpeggiator with step sequencer mode

• Polyphonic step sequencer with up to 64 steps and rests
• Sequencer supports acid-style glide per step
• Sequencer can be used as a modulation source

Hardware

• Tactive™ 37-note slim-key keyboard with polyphonic aftertouch
• 100% analog signal path
• Intuitive, knob-per-function layout
• Spring-loaded pitch wheel with selectable range per program (1 to 12 semitones up and down)

• Pro-quality, all-steel chassis

• 13″ L x 9.88″ W x 2.75″ H (56.2 cm x 25.1 cm x 7.0 cm)
• Weight: 8.76 lbs. (3.97 kg)

Inputs and Outputs

• Main output mono (1/4” jack)
• Headphone output mono (1/4” TRS phone jack)
• MIDI in, out, and thru ports
• USB-C  for bidirectional MIDI communication
• Footswitch/expression pedal input
• Pedal input also supports trigger and gate signals

• Separate power switch
• 12V DC 1.2A power supply, center-positive (included)
• Power supply can be plugged into an AC outlet capable of supplying from 100 V to 240 V at 50 Hz/60 Hz
• 14 Watts maximum power consumption