Sequential Fourm 4-Voice Analogue Synthesiser with Polyphonic Aftertouch

Fourm is a compact analogue synthesiser that invites you to play, shape, and perform with unprecedented expression

Fourm is a compact analogue synthesiser 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.

Fourm delivers four genuine voices of Sequential analogue 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.

Fourm's analogue 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% analogue sound.

Fourm's analogue 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 analogue.

From its solid steel chassis to the custom-engineered Tactive slim-keys keybed with responsive polyphonic aftertouch, every element of Fourm was designed to deliver a fully integrated, high-performance playing experience. It's a no-compromise, all-analog instrument, built for the next generation of synthesists.

Custom-designed by Sequential, the Tactive keybed features 37 slim-keys tuned specifically to complement Fourm's analog synthesis engine. And for the first time in 40 years, Sequential has returned to polyphonic aftertouch, an incredibly expressive performance feature that brings per note articulations to your fingertips.

Polyphonic aftertouch is one of Fourm's most expressive features, offering a direct and nuanced connection between your playing and per note synthesis parameters. It opens up new possibilities for articulation - from subtle dynamics to dramatic gestures - that go far beyond what's possible with other high performance musical instruments and controllers.

Fourm's modulation section is inspired by the legendary Sequential Circuits Pro-One, a highly sought-after classic monosynth that has propelled the bass lines of synthpop for decades. Explore the immediacy and flexibility of this hands-on modulation matrix and let your latest sonic inspirations take Fourm.

Fourm's arpeggiator responds to your playing with inspiring musical results. Need a three octave setting with a dotted 8th note step value to create cascading, syncopated patterns? Fourm can do that and more. With re-latching, repeat settings, and six modes of interaction, the arpeggiator is a powerful tool for spontaneous composition and performance

Tucked into the arpeggiator section, Fourm's polyphonic step sequencer is a creative powerhouse. Yes, it can play back musical phrases - but it can also be used as a modulation source, perfect for triggering rhythmic filter patterns and more. With support for chords, ties, rests, Acid-style per-step glide, and deep modulation routing, the sequencer transforms Fourm into a dynamic, hands-on composition tool.

Synthesis

Two Prophet-5 lineage analogue 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 behaviour
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% analogue 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
22.13? 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 & 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

Specifications