Oscillators
Oscillators are the beating heart of any synthesizer, and in Spirit, they deliver the raw, shapeable sound that fuels everything else. Spirit features two analog oscillators (A and B) plus a noise generator and ring modulator. These sources are always active and are routed to two separate signal paths: one path runs through the Filter and ADSR envelope, the other goes through the Shaper Y section. This dual-routing gives you enormous flexibility for creating layered textures, parallel modulations, or independent sonic behaviors from a single voice.
Oscillator A
WAVEFORM
Oscillator A provides three classic waveforms: triangle, sawtooth, and pulse. It's important to note that the Spirit refers to a pulse wave as a "rectangular wave" and pulse width modulation (PWM) as rectangular width modulation (RWM). The pulse/rectangular wave includes four selectable widths: 50, 30, 15, and 8 percent duty cycle, giving you options from square wave to progressively more narrow pulses for richer harmonic variation.
OCTAVE
The Octave Knob sets the frequency of Oscillator A in organ-style steps: 32', 16', 8', and 4'. The 8' setting is standard pitch (middle C plays as middle C).
SYNC
The SYNC switch hard-syncs Oscillator B to A. When enabled, Oscillator B restarts its wave cycle every time Oscillator A completes one, creating harmonically complex sync tones. This is especially effective when you sweep or modulate Oscillator B’s pitch: Osc B will glitch out in the most musically satisfying way. Use the Octave and Interval knobs to set the harmonic tone. The mod wheel (or any other continuous hardware control) can be assigned to the Pitch knob for real-time sweeps (right-click on the Pitch knob, select MIDI Learn, move the mod wheel, and that's it).
Oscillator B
Oscillator B mirrors A in basic functionality but goes a little rogue with more advanced pitch options for detuning, drone behavior, and modulation. It offers two special range settings, labeled “Bass” and “Wide,” that break Oscillator B free from the keyboard’s pitch control. In Bass mode, it ranges from 30Hz to 300Hz. In Wide, it stretches from 2Hz all the way to 10kHz. That means you can use it like an LFO or audio-rate modulator. When combined with features like oscillator sync you can create everything from locked-in harmonics to full-blown audio mayhem.
WAVEFORM
Oscillator B includes triangle, sawtooth, and pulse (rectangular) waveforms, with its own set of pulse/rectangular wave widths (40, 20, 10, 3) distinct from Oscillator A. This lets you mix harmonics and build more complex timbres easily.
OCTAVE/RANGE
This switch determines how Oscillator B tracks pitch. The first four positions provide standard octave relationships relative to Oscillator A: -1, 0, +1, and +2. The remaining two positions, BASS and WIDE, disconnect Oscillator B from all global pitch controls (keyboard, pitch wheel, master tune). In these modes, Oscillator B becomes a freely tunable source:
BASS range: 30 Hz to 300 Hz
WIDE range: 2 Hz to 10,000 Hz
These two settings useful for drones, audio-rate modulation, or an additional LFO.
INTERVAL
This control detunes Oscillator B sharp or flat when the Octave/Range switch is set to one of the four octave step positions. It spans up to a little over a fifth in either direction. At center, there’s no transposition. Small deviations from center add gentle detuning. In BASS and WIDE modes, INTERVAL becomes a continuous frequency control with full-range sweep.
Noise Generator
The Spirit includes a versatile Noise Generator that offers three distinct types of noise: White, Pink, and Red. These can be used either as audio sources or as modulation sources. Use it to create everything from classic snare and hi-hat textures to chaotic filter sweeps or unstable pitch modulations. The different flavors of noise each have their own spectral characteristics: White noise is evenly distributed across the frequency spectrum, Pink noise rolls off slightly for a warmer, more natural tone, and Red noise... well, that one’s a bit of a wild card.
The original Red noise circuit in the 1980s Spirit hardware was based on the infamous MM5837 chip, a pseudo-random sequence generator better known for its eccentric behavior than its precision. Rather than producing true randomness, it repeats a very long, irregular pattern that can lend a strange, twitchy character when used to modulate oscillator pitch, filter cutoff, or pulse width. Cherry Audio’s virtual Red noise faithfully emulates this behavior, preserving its glitchy, semi-chaotic charm. It’s unpredictable in all the right ways and can lead to some surprisingly musical happy accidents.
Ring Modulator
The Spirit's Ring Modulator is a classic dual-input amplitude modulator that multiplies two signals together to produce a new, often harmonically rich signal containing the sum and difference of the input frequencies. The result? Metallic clangs, robotic tones, and otherworldly textures that are impossible to achieve with traditional mixing or filtering. Spirit's ring modulator is particularly effective when combining a sine or triangle wave with a detuned oscillator, or when pairing an audio-rate oscillator with one of the built-in noise sources for more chaotic, percussive effects.
In keeping with the design philosophy of the original Spirit hardware, this ring modulator delivers a raw, analog-style character that rewards experimentation. Use it subtly to add a shimmering edge, or crank it for full-blown sci-fi dissonance.