Overtone

Additive synthesis VCO that builds waveforms from the harmonic series.

Overtone generates sound by summing sine waves at integer multiples of a fundamental frequency. The fundamental is always present; eight toggle switches enable individual overtones (harmonics 2 through 9), each scaled by natural 1/n amplitude falloff. Toggle them all on for an approximation of a sawtooth wave; turn them all off for a pure sine. The combinations between are where additive synthesis lives — each switch combination produces a distinct timbre with its own character.

10 HP. Monophonic audio output.

How additive synthesis works

Any periodic waveform can be decomposed into a sum of sine waves at integer multiples of its fundamental frequency. A sawtooth wave at 100 Hz is the same thing as adding sines at 100, 200, 300, 400 Hz… each at amplitude 1/n. A square wave is the same thing as adding only the odd harmonics: 100, 300, 500, 700 Hz…

Overtone reverses this: instead of generating a complex waveform and trying to filter parts of it out, you build the timbre directly by choosing which harmonics to include. Want a square-like sound? Set the filter to “Odd” — only odd-numbered harmonics (1, 3, 5, 7, 9) will sound. Want something between a sine and a saw? Just toggle on the harmonics that interest you.

This gives you direct timbral control without filters, distortion, or wavetable scanning. Every switch combination is its own distinct waveform.

Controls

Inputs

Output

The output is dynamically normalized — the amplitude of all active harmonics (including the fundamental) is summed and the result is divided by the sum of their 1/n weights, then scaled to ±5V. This means toggling harmonics on or off doesn’t change the overall output level — only the timbre.

Harmonic amplitude falloff

This 1/n falloff matches the natural harmonic series of physical instruments (and matches the Fourier series of an ideal sawtooth wave). Higher harmonics contribute progressively less to the overall sound, so toggling harmonic 9 produces a much subtler change than toggling harmonic 2.

LED indicators

Above each switch is a red LED that shows the actual active state of that harmonic — taking into account both the toggle position and any CV overrides (Mask CV, Filter CV). When the Mask CV is patched and overriding the toggles, the LEDs track the CV-driven state. When the Filter is set to Odd, the LEDs above even harmonics will be off even if their toggles are on.

This gives you immediate visual feedback on what’s actually sounding regardless of where the control signal is coming from.

Zero-crossing gating

When you toggle a harmonic on or off, the change doesn’t happen instantly — it waits until that harmonic’s sine wave crosses zero, then transitions cleanly with no discontinuity. This eliminates clicks completely without using a fade envelope (which would cause amplitude artifacts).

Higher harmonics cross zero more frequently (harmonic 9 crosses 9× per fundamental cycle), so they respond almost instantly. The fundamental takes at most half a cycle to find a crossing point, which at C4 is about 1.9 ms — imperceptible.

The waveform display

The display shows several layers:

• Bright blue stroke — the composite waveform being generated, in real time
• Faint colored traces — the individual sine waves of each active harmonic, each in a different hue
• Faint white trace — the fundamental sine wave (always present)
• Dark background with center line — zero crossing reference

The display only recomputes when the harmonic selection changes, so it’s efficient even at high frame rates. You can see exactly how the composite waveform is constructed from its harmonic components.

Mask CV modes

The Mask CV input has two interpretation modes, selectable from the right-click context menu:

Binary mode (default)

Voltage 0–10V is mapped to an 8-bit integer (0–255). Each bit controls one harmonic:

• Bit 0 (least significant) = Harmonic 2
• Bit 1 = Harmonic 3
• Bit 2 = Harmonic 4
• Bit 3 = Harmonic 5
• Bit 4 = Harmonic 6
• Bit 5 = Harmonic 7
• Bit 6 = Harmonic 8
• Bit 7 (most significant) = Harmonic 9

Sweeping the CV creates rapid, complex timbral changes as the bit patterns shift through every possible combination. Each step is approximately 0.039 V (10V / 255).

Patch a sequencer or sample-and-hold to the Mask input to step through specific timbral combinations. Each integer voltage value maps to a unique waveform.

Sweep mode

Voltage 0–10V is mapped to a count of harmonics enabled from the bottom up:

Sweeping the CV produces a smooth brightness change — like a low-pass filter sweep, but built from actual harmonics rather than spectral filtering. Patch an envelope generator to the Mask input for harmonic-based dynamic timbral evolution.

Patch ideas

Sub bass + harmonic morphing

Set Freq to a low octave (-2 or -3). Patch a slow LFO to the Mask CV in Sweep mode. The bass note slowly grows brighter and darker as harmonics are added and removed.

Stepped timbral sequence

Patch a sequencer or random source to the Mask CV in Binary mode. Each step lands on a different harmonic combination — every step has a unique timbre while the pitch stays constant. Combine with a slow V/Oct sequence for melody with constantly evolving tone.

Filter swap

Patch a stepped CV (sample-and-hold from a clock) to the Filter input. The harmonic content flips between All / Odd / Even on every clock pulse — instant timbral shifts that mimic radical filter changes.

Sine-to-saw envelope

Patch a slow attack envelope to the Mask CV in Sweep mode. Each note starts as a pure sine and grows into a saw wave as the envelope rises — like a wavetable sweep but built from real additive synthesis.

FM-style sidebands

Set the toggles to a sparse pattern (e.g., harmonics 2, 5, 9). The result is a metallic, FM-like timbre because the active harmonics form a non-harmonic-feeling subset of the series. Modulate Freq with V/Oct for melodic playing.

Full mask voltage table (Binary mode)

The table below shows every possible value of the Mask CV in Binary mode. Each integer step (~0.039 V) corresponds to a unique 8-bit pattern, which determines exactly which overtones (2-9) are active. The fundamental (1) is always present regardless of the mask value.