SEQUENTIAL Fourm

Sequential Fourm is a 4-voice polyphonic analog synthesizer that combines the classic Sequential tone with maximum expressive performance. The control panel, inspired by the historic Pro-One, puts modulations at your fingertips, eliminating annoying menus. The slim 37-key keyboard with polyphonic aftertouch opens up new expressive techniques. The sound synthesis architecture uses two oscillators and an LFO, allowing you to select all waveforms simultaneously. The classic 4-pole low-pass filter with resonance is supported by low-frequency compensation. There are two ADSR envelopes, and the arpeggiator also offers a sequencer mode.

The Sequential sound in a compact format

At the heart of Fourm is the Prophet DNA, with two oscillators per voice with simultaneously selectable waveforms and a classic 4-pole resonant low-pass filter enhanced by bass compensation, which preserves depth and presence even at high resonance values. The 100% analog signal path, complemented by highly responsive envelopes and an aggressive drive/feedback circuit, delivers the same sonic power that made Sequential famous, in a portable and intuitive format.

Compact and extremely expressive

The slim 37-note keyboard with polyphonic aftertouch opens up innovative control techniques: note bending, swell on individual voices, dynamic nuances, etc. This expressiveness makes the Sequential Fourm not only a studio instrument, but also a stage companion capable of responding to touch dynamics with naturalness.

Fourm sound generation section

The Fourm's synthesis engine is based on two voltage-controlled analog oscillators (VCOs) for each voice. Oscillator A generates sawtooth and square waveforms, while Oscillator B also offers a triangle option. All waves can be activated simultaneously, allowing for rich and complex timbral combinations. Pulse Width Modulation (PWM) is available on both oscillators, with a wide range of adjustment options, up to changing the phase of the waveform. Oscillator B also has two "LO" modes that transform it into a polyphonic LFO source, with or without key tracking, ideal for dynamic pitch and filter modulations. The hard sync function allows you to synchronize the subordinate oscillator to the cycle of the other, generating aggressive and harmonically complex tones. In combination with variable pitch and fine detune, you can switch from classic Prophet tones to modern, incisive sounds.

Envelopes and dynamic control in the Fourm

The Sequential Fourm has two independent ADSR envelope generators, dedicated to the filter and amplifier respectively. The filter envelope shapes the cutoff over time, with attack, decay, sustain, and release allowing you to sculpt the brightness and body of the sound with precision. The velocity amount option also allows you to link the dynamics of your touch on the keyboard to the opening of the filter, making your performance more expressive and natural. The amplifier envelope shapes the volume of the sound, reproducing time curves ranging from soft attacks for more ethereal pads to percussive hits with instant attack. Both envelopes can be re-triggered with each key press, allowing for more complex articulations and accurate control in fast phrases. This section, in combination with the oscillators and modulation matrix, provides the sound designer with extreme flexibility, capable of covering both classic timbres and advanced experimentation

The Sequential Fourm modulation matrix

The Fourm inherits a direct modulation matrix from the Pro~One, enhanced and made more intuitive. There are three main sources (filter envelope, Oscillator B, LFO) that can be routed to eight selectable destinations on the panel, including Cut-Off, amplitude, pitch, and pulse width of the oscillators. Each source can be routed to either the direct bus (red LEDs) or the Mod Wheel bus (blue LEDs), with the possibility of simultaneous reception (purple LEDs). The modulation intensity can be set to positive or negative values, making the envelopes and interactions between modulators extremely flexible. The integrated LFO, capable of covering frequencies from 0.021Hz to 556Hz, offers triangular, square, sawtooth (also inverted), sample & hold, and even noise sources in different colors (white, pink, purple). This section allows for subtle and musical modulations as well as more extreme effects, while keeping complexity under control thanks to the intuitive logic of the buttons and color-coded indicators.

Performance, integration, robustness

The Arpeggiator/sequencer can also be synchronized to an external clock and, in addition to the classic presets (up, down, random, etc.), it gives you the ability to program complex patterns, thanks to the 303-style glide per step, ideal for applying variations and making bass or lead lines less static. A creative tool even for the most modern electronic production. Included are 128 factory presets ready to use or as a starting point for your own timbre research and programming. Connectivity includes dedicated audio outputs (Main Out mono ¼" jack and TRS headphone output), classic triad (In, Out, and Thru) MIDI DIN and USB-C, as well as inputs for pedals and a steel chassis with anti-theft slot, for absolute reliability on tour and in the studio. With Fourm, Sequential makes true analog synthesis accessible to everyone with modern features useful in both the recording studio and live performances. Its panel is "knob-per-function," with no menus: each control has its own dedicated knob or button. This direct approach is a strength highly appreciated by musicians who want immediacy and total control during sound design and performance.