The Moog Spectravox is a versatile semi-modular spectral processor that combines the functionality of an analogue vocoder, filter bank, and synthesizer voice in a compact 60HP Eurorack-compatible format. Part of Moog's acclaimed semi-modular range alongside the Mother-32, DFAM, Subharmonicon, and Labyrinth, the Spectravox offers unique sonic possibilities that extend far beyond traditional vocoder applications.

Core Functionality

Multi-Function Design

The Spectravox operates as three distinct instruments in one unit:

Analogue Vocoder: Features dual filter banks with 10 bands each - a Program (analysis) bank for processing input signals and a Carrier (synthesis) bank for shaping the output. Unlike many digital alternatives, this is a true analogue vocoder with character reminiscent of early Wendy Carlos and Moog collaborations from the late 1960s.

Spectral Filter Bank: Can function independently as a sophisticated filter bank, offering tone-shaping capabilities that bridge the gap between traditional synthesizer filters and EQ. The filter bank features overlapping 6dB/octave slopes with bands at 230, 320, 560, 830, 1200, 1700, 2300, 3200, 4500, and 5400 Hz (at default Shift position).

Synthesizer Voice: Includes a complete oscillator section with sawtooth and variable-width pulse waves, plus white noise source, making it a capable standalone synthesizer or carrier source for vocoding.

Unique Features

Spectral Shift: A standout feature allowing real-time frequency shifting of all filter bands simultaneously. This can be controlled manually or via the built-in triangle-wave LFO (0.05Hz to 500Hz), enabling phaser-like sweeps, resonant effects, and dynamic spectral manipulation impossible with fixed filter banks.

Variable Resonance: Each filter band offers adjustable resonance, adding harmonic content and allowing the filters to act almost like resonators. This capability was absent from the original Moog 907 Fixed Filter Bank that inspired the design.

Extensive Patchbay: 36 patch points (19 inputs, 17 outputs) provide comprehensive CV control over individual filter bands, envelope followers, and VCA inputs, enabling complex routing and creative sound design possibilities.

Sound Character

The Spectravox imparts a distinctive "baked-in" coloration to all signals passing through it, creating a characteristic scooped, warm, and buzzy quality. This inherent harmonic signature is an integral part of its sound, making it ideal for creative sound design, special effects, and experimental synthesis rather than transparent signal processing.

Vocoder Performance

While the vocoder produces rich, smooth tones with strong character, vocal intelligibility is deliberately limited, reflecting the characteristics of early analogue vocoders. A Hiss/Buzz switch helps with fricatives and sibilance by routing white noise to the upper frequency bands when triggered by unvoiced elements.

Filter Bank Applications

As a filter bank, the Spectravox excels at dramatic tone transformation, creating everything from vocal tract-like sounds to phaser effects. The combination of individual band attenuation, spectral shifting, and resonance control offers unprecedented real-time spectral manipulation capabilities.

Design & Construction

The Spectravox maintains Moog's high build quality standards with professional-grade construction in a compact desktop format. The front panel can be removed and installed in a standard Eurorack system, though it requires external power when rack-mounted (450mA from +12VDC rail).

The unit features minimal external connections - a rear-panel quarter-inch output (doubling as headphone output) and front-panel XLR/jack combo input with preamp suitable for dynamic microphones (no phantom power provided).

Applications

The Spectravox excels in creative and experimental applications:

• Unique vocal effects and robot voices
• Complex filter sweeps and spectral processing
• Synthetic percussion and special effects
• Modular synthesis sound source
• Real-time spectral manipulation
• Ambient textures and sound design

While it may not be the first choice for conventional subtractive synthesis or highly intelligible vocoding, its distinctive character and unprecedented flexibility make it invaluable for exploratory music-making and sound design.

Technical Specifications

Sound Generation

• VCO: Single oscillator with sawtooth and variable-width pulse waves
• Frequency Range: 10Hz to 4kHz
• Pitch Tracking: Accurate 1V/octave over wide range
• Noise Source: White noise generator with variable VCO/Noise mix

Filter System

• Filter Banks: Dual 10-band filter arrays (Program and Carrier)
• Filter Types: 1 Low-pass, 8 Bandpass, 1 High-pass (per bank)
• Filter Slopes: 6dB/octave (overlapping)
• Resonance: Variable per band (non-self-oscillating)
• Frequency Centers (default): 230, 320, 560, 830, 1200, 1700, 2300, 3200, 4500, 5400 Hz
• Spectral Shift: Continuous frequency shifting of all bands
• Band Control: Individual attenuation per band (cut only)

Modulation

• LFO: Built-in triangle wave LFO
• LFO Rate: 0.05Hz to 500Hz (approximately)
• LFO Destination: Hardwired to Spectral Shift function
• Envelope: Decay-only envelope generator (instant attack, variable decay, no sustain)

Additional Features

• Hold Function: Spectral freeze capability with manual and CV trigger
• Threshold Trigger: Envelope trigger from Program signal level
• Cross-patching: Individual CV control over all filter bands
• Feedback Routing: Internal feedback possibilities via patchbay
• Level Matching: Requires external attenuation for Eurorack signal levels

Connectivity

• Patchbay: 36 × 3.5mm jacks (19 inputs, 17 outputs)
• Audio Input: XLR/1⁄4" TRS combo jack with preamp (line/instrument level)
• Audio Output: 1⁄4" TRS (headphone) / 1⁄4" TS (line output)
• CV Input Level: 1.7V (line level, not Eurorack 5V standard)

Control Interface

• Format: 60HP Eurorack-compatible front panel
• Controls: Rotary potentiometers with option for knurled upgrade kit
• Switches: 3-position mode selection switches
• Indicators: LED level indicator for input signal

Power Requirements

Standalone Operation

• Power Supply: External wall adapter (included)
• Input: 100-240VAC, 50-60Hz
• Output: +12VDC, 2.0A
• Consumption: 4.8 Watts
• Connection: Barrel connector (center-pin positive)

Eurorack Operation

• Current Draw: 450mA maximum from +12VDC rail
• Power Header: 10-pin Eurorack standard
• Module Depth: 1.5 inches

Physical Specifications

• Width: 60HP (12 inches / 304.8mm)
• Depth: 1.5 inches (38.1mm) when rack-mounted
• Security: Kensington lock slot
• Construction: Professional-grade components and build quality