The GS e7 is a seven-voice polyphonic analog synthesizer based on subtractive synthesis, with a fully analog sound generation path. Each voice is built around two voltage-controlled oscillators (VCO), a white noise source, a mixer, a voltage-controlled filter (VCF), and a voltage-controlled amplifier (VCA). Control signals are generated digitally by a microcontroller capable of running three low-frequency oscillators (LFO) and two ADSR-type envelope generators (EG). An onboard stereo digital effects processor handles both chorus and delay. The interface was designed to be simple and intuitive, with MIDI connections, USB, balanced stereo audio outputs, a headphone output, and CV inputs.

Signal Path

The signal path is completely analog, featuring two VCOs per voice alongside a white noise source, a mixer, a 4-pole low-pass voltage-controlled filter, and a VCA. Control voltages are digitally generated and include three LFOs and two ADSR-type envelope generators. A stereo digital effects processor with delay and chorus completes the signal chain. LFO 1, LFO 2, and the delay can all be synced to an incoming MIDI clock signal using a user-selectable subdivision.

Oscillators

Each voice features two VCOs plus a sub oscillator. Each oscillator offers three waveforms: triangle, sawtooth, and saw-tri (a blend of triangle and sawtooth). Fine-tuning and transpose controls are available, with transpose adjustable up to ±2 octaves. Oscillator pitch can also be modulated by any of the three LFOs or by EG1.

In addition to the main waveforms, each oscillator has an independent pulse wave that can be switched on or off and mixed freely with the other waveforms. Pulse width can be modulated by LFO1 and/or EG1.

The two oscillators can be hard synced, with oscillator 1 acting as the master and oscillator 2 as the slave, enabling classic sync timbres. The GS e7 includes an autotuning algorithm that completes in approximately 2 seconds, tuning all voices in parallel for a much faster process than conventional sequential approaches.

Mixer

The mixer allows independent level control and blending of the two oscillators, the sub oscillators, and the white noise source. When an external audio signal is connected via the external input, the white noise source is automatically disabled and replaced by the external input, which can then be mixed alongside the oscillators.

Filter

The GS e7 uses a 4-pole ladder-type low-pass filter with resonance control, operating at 24 dB/octave. Filter cutoff can be modulated by EG1, with the modulation depth also sensitive to velocity. Any of the three LFOs can additionally be routed to the filter for cyclic modulation. Keyboard tracking is available, adjusting the cutoff frequency relative to the note played. The filter also responds to the modulation wheel and aftertouch for real-time expressive control.

Chorus

Two distinct chorus algorithms are available. The Basic chorus is subtle, adding spatiality and width to the sound using two delay lines, each with its own internal LFO. The Ensemble chorus uses four delay lines, each with a dedicated internal LFO, to simulate the character of a string or vocal ensemble, adding a richer and more complex dimension to the sound. Both algorithms offer controls for rate, depth, and mix.

Delay

The delay can operate either as a standard stereo delay or as a ping pong delay, with a maximum delay time of 1.35 seconds. The delay can be synced to the MIDI clock, in which case the delay time knob controls the rhythmic subdivision rather than the absolute delay time. Feedback and mix are independently controllable.

LFOs

Three LFOs are available. LFO 1 and LFO 2 each offer five waveforms: triangle, ramp up, ramp down, square, and random with sample and hold. LFO 3 provides the first four waveforms and is activated by the modulation wheel and/or aftertouch. All LFOs span a frequency range from 0.1 Hz to 100 Hz.

LFO 1 and LFO 2 support six operating modes:

• Monophonic: The LFO runs in phase across all voices simultaneously.
• Polyphonic: A slightly different frequency is generated for each voice, causing phase interactions that produce more complex and evolving modulations.
• Keyboard Tracking (KB Tracking): The LFO frequency scales with the note played, following the chromatic scale.
• Keyboard Sync (KB Sync): The LFO restarts each time a key is pressed, with each voice maintaining its own independent LFO.
• Clock Sync: The LFO frequency locks to the incoming MIDI clock, with automatic BPM detection and configurable rhythmic subdivisions.
• Keyboard + Clock Sync: The LFO frequency follows a subdivision of the MIDI clock and also restarts on each key press.

Envelope Generators

Two ADSR-type envelope generators provide control over attack, decay, sustain, and release. Velocity can independently affect the attack and release times. Envelope times also respond to keyboard tracking, scaling with the note played for more natural dynamic behavior across the keyboard range.

Stereo

By default, the voices are spread in a stereo panorama from left to right. The stereo spread can be adjusted to center all voices, reverse the panning from right to left, or set any position in between. A stereo motion option enables the stereo spread itself to be modulated by an LFO, creating dynamic movement in the stereo field.

Presets

The GS e7 can store up to 640 presets in total, of which 128 are multitimbral presets.

Multitimbral Operation

The GS e7 supports up to four multitimbral parts simultaneously. Each part carries its own complete sound configuration and can be assigned an independent MIDI channel, keyboard zone, velocity zone, transpose setting, and MIDI filter. Voice allocation is flexible: each part can be assigned a dedicated number of voices, or voices can be shared between parts.

MIDI Polyphonic Expression (MPE)

The GS e7 supports MIDI Polyphonic Expression, enabling per-note control of dimensions such as pitch and filter cutoff independently for each voice. MPE compatibility has been tested with GeoShred.