Sequential Fourm

Posted on September 27, 2025October 8, 2025 by admin

The Sequential Fourm is a compact, four-voice analog polyphonic synthesizer with full analog signal path and a custom polyphonic aftertouch keybed. It is positioned by Sequential as their most affordable synthesizer to date and the first Sequential instrument in about 40 years to restore polyphonic aftertouch.

It draws architectural inspiration from the Prophet-5 heritage, and combines that with a hands-on interface (knob-per-function and top-panel modulation matrix) for expressive performance and sound design.

Key Features & Specifications

Here is a consolidated list of features and specs of the Fourm:

Sound Engine & Oscillators / Filter / Modulation

100 % analog signal path (no DSP in the audio path)
4 polyphonic voices
Two analog oscillators per voice:
- Each oscillator supports multiple waveforms (simultaneously selectable)
- Oscillator B can also be used in a low-frequency mode (i.e. functioning as an LFO)
- Classic sync mode (Prophet-style) is supported
- Pulse width modulation (PWM) available on square waves
4-pole resonant low-pass filter (based on Prophet-5 revisions) with bass compensation (to maintain low-end clarity even at high resonance)
The filter can self-oscillate via resonance and includes keyboard tracking options (quarter, half, full)
Feedback/drive circuit for adding edge/grit to the signal path
Noise generation (white, pink, violet) included
Envelopes: Two 4-stage ADSR envelopes — one for filter, one for amplitude
LFO: One global LFO with multiple wave shapes (sine, saw, reverse saw, square, sample & hold, noise, DC) and can be synced to tempo
Modulation architecture:
- Top-panel modulation matrix (a la Pro-One) with button-based routing (no deep menu navigation)
- Two modulation buses with multiple sources/destinations, combinable routing
- Polyphonic aftertouch destinations: oscillator A freq, oscillator B freq, filter cutoff, amplitude, LFO frequency, LFO amount — up to six destinations simultaneously selectable
- Aftertouch matrix / routing available top-panely
Glide / portamento features (including different glide modes)
Unison (monophonic) mode: you can stack voices (from 1 to all 4) plus chord memory
Vintage mode: adds voice-to-voice component variation to simulate vintage hardware behavior

Interface, Keyboard & Performance

Tactive™ 37-note slim-keys keyboard, custom-built by Sequential, with polyphonic aftertouch and velocity sensitivity
Pitch wheel (spring-loaded) with selectable bend range (±1 to ±12 semitones)
Modulation wheel, routable via modulation routing
OLED display for browsing presets, categories, and accessing deeper settings not directly on panel
Knob-per-function layout on the front panel for immediate access to synthesis controls (oscillator, filter, envelopes, LFO, etc.)

Sequencer, Arpeggiator & Modulation Tools

Arpeggiator with six modes, octave settings, repeat options, and with re-latching/repeat control
Polyphonic step sequencer (up to 64 steps) with support for chords, rests, ties, and per-step glide (acid-style)
The sequencer can act as a modulation source (i.e. modulating filter cutoff, oscillator, etc.)
Modulation matrix sources include filter envelope, oscillator B, LFO, and aftertouch
Destinations include oscillator frequencies, pulse widths, filter cutoff, amplitude, LFO freq, LFO amount

Hardware, Connectivity & Physical

Steel chassis (robust, all-steel)
Dimensions: 22.13″ × 9.88″ × 2.75″ (56.2 cm × 25.1 cm × 7.0 cm)
Weight: ~ 8.76 lb (3.97 kg)
Audio outputs:
- Main (¼″ mono output)
- Headphone output (¼″ TRS)
MIDI: DIN MIDI In, Out, Thru and USB-C (bidirectional MIDI)
Pedal / expression input (supports footswitch, expression pedal, triggers / gate)
Power:
- 12 V DC, 1.2 A, center-positive (supply included)
- AC input supports 100 V to 240 V, 50/60 Hz
- Max power draw ~14 W
Optional security lock (chassis lock) for institutional / retail settings

Presets, OS & Updates

Factory and User memory:
- Two factory banks (F1, F2) and two user banks (U1, U2)
- Banks F2 and U2 are duplicates of a “basic programs” set of 128 programs (i.e. as shipped the factory/user presets are identical)
- Sequential plans to release a new set of factory sounds in October 2025 (free download)
Operating System: The initial OS is version 1.0.0.2 (or “install this update”) for bug fixes on launch
Documentation, user guide, and sound lists are available on Sequential’s website