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.
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.
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.
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.
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.
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Because polyphonic aftertouch is still relatively uncommon, there’s not much guidance out there on how to use it effectively. That’s why we’ve put together a list of techniques — and you don’t need to be a virtuoso player to benefit. This guide is for anyone curious about what polyphonic aftertouch can bring to their music.
Discover easy ways to integrate polyphonic aftertouch into your playing — no virtuoso skills required. In this video, Glasys explores a range of expressive techniques in a way that’s intuitive and accessible. In just a few minutes, you’ll learn new methods to shape your sound and deepen your musical expression.
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.
“The polyphonic aftertouch is seriously so fun… Sequential nailed it.”
Bryn Bliska, Keyboardist –
Chappell Roan, Jacob Collier
“…it’s amazing to have a pro, vintage sound in such a small package!“
Nicholas Semrad, Keyboardist –
Lauryn Hill, Empire of the Sun
“…polyphonic aftertouch on speed-dial. A perfect little synth.”
Peter Dyer, Keyboardist –
Katy Perry, American Idol, CAPCOM
Inspired by the Pro~One, Fourm’s top-panel modulation matrix puts deep sound design at your fingertips. Sources and destinations are clearly labeled, connections are made with a button press, and color-coded indicators keep even complex routings intuitive.
Fourm’s polyphonic aftertouch allows each note to respond independently to pressure, giving you deeper control over expression from the keyboard. Easily route poly aftertouch to key synthesis parameters directly from the top panel.
Fourm features a smooth, responsive pitch wheel with controls for adjusting bend range. Route the mod wheel to multiple destinations using nearby modulation controls.
Browse presets by name and category with a crisp, high-contrast OLED screen. You can also access even deeper synthesis features that don’t appear on the panel.
Stack up to four voices on a single note for bold, monophonic sounds. Adjust unison detune to dial in the perfect amount of thickness and texture.
Control the transition time between notes to create smooth pitch glides instead of instantaneous changes. Perfect for expressive articulations like bass slides.
Fourm features two analog oscillators that evoke the iconic tone of the Prophet-5. Select multiple waveshapes at once to create a wide variety of rich, layered timbres.
Choose from a wide range of modulation shapes — and stack multiple waveforms simultaneously for complex, modern textures that add distinctive motion to your sound.
Fourm’s custom 37-note slim-keys keybed with polyphonic aftertouch was developed to work in concert with Fourm’s analog synthesis engine. Every element was co-designed and precisely calibrated to unlock new levels of expression and creativity.
Shape your tone with drive-boosted feedback for additional edge and fullness. Blend in white, pink, or violet noise to introduce color and character to your sound.
Based on the legendary Prophet-5 design, Fourm’s 4-pole resonant low-pass filter shapes your sound with warmth and character. And with built-in bass compensation, you can crank the resonance without losing low-end power — all with unmistakable Sequential tone.
Explore six classic arp modes with octave and repeat settings. And polyphonic aftertouch adds a new layer of expression, letting you accentuate individual notes as the pattern plays.
Fourm’s secret superpower is a polyphonic step sequencer that supports chords, rests, ties, and Acid-style per-note glide. And quickly switch modes to direct the sequencer to the filter or other timbral effects for instantly musical modulations.
Fourm includes two 4-stage envelopes (attack, decay, sustain, release) modeled after the Prophet-5’s response curves. Use them to shape tone, volume, and modulation over time for dynamic, expressive sound design.
Secure your Fourm with a built–in chassis lock. Great for educational and retail institutions.
As with the Prophet-5, Fourm features a single, unbalanced ¼ inch audio output jack for mono signals as well as a headphone out.
With standard MIDI in/out/thru and USB-C, Fourm integrates easily into your setup — whether you’re connecting to other hardware instruments or your DAW.
Connect a foot switch to sustain notes, or create volume swells and filter sweeps with an expression pedal. Foot pedals add more depth and dimension to your performance.
Some of our products can expose you to chemicals including BPA, which is known to the State of California to cause cancer and birth defects or other reproductive harm.
Though independent laboratory testing has certified that our products are several orders of magnitude below safe limits, it is our responsibility to alert you to this fact and direct you to https://www.p65warnings.ca.gov for more information.
