Digital oscillator with envelope and VCA/LPG

The Algorithmic Oscillator is a Buchla-format VCO based on Plaits by Mutable Instruments. The successor to the 1979 DAO, the AO has more knobs, more parameters, and more I/O than the DAO plus new features not present on Plaits. With an internal envelope generator and a simulated LPG with adjustable vactrol response, the AO is an ideal standalone voice module for small Buchla systems.

Core Features

• High-fidelity digital oscillator (48 kHz, 16 bit)
• 24 synthesis algorithms (see the Algorithm List below)
• Auxiliary output with complementary audio signal
• Internal VCF/A with variable LPG mode
• Voltage-controlled decay envelope*
• Dedicated knobs for envelope decay and VCF/A amplitude*
• Pitch quantizer (1/4 tone, semitone, harmonic, and octave options)*
• Inverting attenuators for all CV inputs (0-10V range)*
• Envelope CV output (0-10V range)*

* = Upgraded features not available on Plaits

Quick Reference

Algorithm selection. Tap the ALGO switch to cycle through the 8 algorithms in each bank. Press and hold the ALGO switch for a few seconds to cycle through the green, yellow, and red banks. See the Algorithm List below for more info on each algorithm. You can also modulate the current algorithm using the Algo CV input. Try this with a sequencer to make a new selection with each step. This works well with the drum models, for example, allowing you to switch between kick, snare, and cymbal for each step of the sequence. Patching in a random CV source (such as the 1979 SVG) is also recommended.

LPG/VCA balance. On modules like the Buchla 292 there's a switch to toggle between VCA and VCF/A (LPG). The AO allows you to crossfade between the two amplifier types instead. Press the Trig switch and turn the Amplitude knob to change the LPG/VCA balance. This is visualized on the top row of LEDs in the Algo section. Turn left for LPG, turn right for VCA. Audio is routed through the LPG only when the Trig switch is on. When the Trig switch is off, audio is passed through the VCA only. When the LPG is activated, the Decay knob will control the "ringing" of the simulated vactrol (altering audio frequency content) along with the envelope decay time (altering audio amplitude). Note that certain algorithms (red bank D-H) do not include the LPG option and will always use the VCA.

Quantizer options. Press the Trig switch and turn the Frequency knob to choose the quantizer mode. The mode is visualized on the bottom row of LEDs in the Algo section. When the quantizer is off, none of the LEDs are illuminated. Turning the knob to the right selects one of four modes: quarter tone (1/2 of a semitone), semitone (12-TET), harmonic series (with the base frequency controlled by the fine-tune knob across a range of approximately 30-120 Hz), and octave. When any of the four quantization modes is enabled, CVs patched to the Pitch input will snap to the nearest semitone or octave. CVs patched to the Freq input are not quantized. This allows for fine tuning, transposition, or microtonal modulation of quantized pitches.

Envelope output. Plaits has an internal modulation schema which routes the internal decay envelope to certain unpatched CV inputs. Although this is not possible with the banana jacks on the AO, you can now patch the envelope CV output to any or all of the CV inputs on the AO (or other modules) and use the envelope as a voltage-controlled modulation source (Plaits does not include a CV input for the envelope decay time).

FM attenuator. When the FM audio input is unpatched, the FM knob works as a fine-tune pitch control. When this input is patched, the FM knob becomes an inverting attenuator, with a 180° phase shift on the FM source when this knob is turned to the left of center.

User data upload. Using just an audio cable, you can upload custom wavetables (green bank algo F), DX7 patches (yellow banks C/D/E), and waveterrain data (yellow bank algo F). Use the web-based Plaits Editor created by Mutable Instruments to generate custom data, which can be downloaded or played back directly from your web browser. To load user data into the AO, select the oscillator model= you want to modify. Only the five models mentioned above accept user data uploads. Connect a 3.5mm cable between your computer/phone and the FM input jack of the AO. Press the Trig switch for five seconds. The "A" LED will turn yellow and start to blink. Maximize the volume on your computer/phone, ensuring that the microphone and any background sounds are muted. Now play back the audio. This takes about 30 seconds. You will see the LEDs on the AO progressively illuminate as the data is downloaded. Once the upload is complete, you can use your custom sounds. There are three quirks to this process. One is that only one of the five user data slots can be active at a time. Uploading user data to one slot will cause user data uploaded to any other slot to be erased. Two is that that user data is not permanently stored in the module's memory. Finally, only the five user data slots mentioned above accept user data. Uploading user data to any of the other oscillator models will do nothing, and all 8 of the LEDs will blink red. This also happens if the user data file is malformed or if the upload otherwise fails. If this happens, press the Algo switch to exit user data upload, or press the Trig switch to try again.

Algorithm List

Dual oscillator. Mix of two analog-style waveforms: a variable-width pulse and a second oscillator which can be continuously waveshaped from triangle to a glitchy sawtooth. Turn the Timbre knob fully to the left to silence the pulse, or turn the Morph knob fully to the right to silence the tri-saw waveform. This technique can be used to take one or both waveforms out of the mix. The AUX output is the sum of the two waveforms with hard sync applied.

Timbre:
Pulse width shaper

Harmonic:
Relative detuning ratio

Morph:
Tri-saw shaper

Waveshaping oscillator. An asymmetric triangle wave is routed through a waveshaper and a wavefolder. The AUX output is similar but uses a different wavefolding method. Both outputs are reminiscent of classic Buchla/Serge textures.

Timbre:
Waveshaper waveform

Harmonic:
Wavefolder amount

Morph:
Waveform asymmetry

2-Operator FM. Two sine oscillators with cross-modulation of phase. The AUX output is a suboscillator derived from the base frequency.

Timbre:
Modulation index

Harmonic:
Frequency ratio

Morph:
Feedback level/type

Granular formant oscillator. Simulation of formants using the multiplication, addition, and synchronization of sine wave segments. The AUX output is a simulation of filtered waveforms by windowed sine waves

Timbre:
Formant frequency

Harmonic:
Frequency ratio

Morph:
Formant width/shape

Harmonic oscillator. An additive mixture of harmonically-related sine waves. The AUX output uses specific frequency ratios (1, 2, 3, 4, 6, 8, 10, 12) which emulate the drawbars on old organ/string synths.

Timbre:
Number of harmonics

Harmonic:
Harmonic emphasis

Morph:
Harmonic shapes

Wavetable oscillator. Four banks of waveforms arranged in an 8x8 matrix. Left of center, the Harmonic knob scans through the four banks with interpolation between waveforms. Right of center, the waveforms are not interpolated. The AUX output is a lo-fi version of the main output with 5-bit resolution. As of Firmware V2 the wavetable algo can accept custom wavetables. See the "User data upload" section above for instructions.

Timbre:
Row index (X-axis)

Harmonic:
Bank selection

Morph:
Column index (Y-axis)

Four-note chords. Tuned waveforms emulate vintage string/organ machines with four-note polyphony. The AUX output provides only the root note of the chord.

Timbre:
Inversion/Transposition

Harmonic:
Chord type

Morph:
Waveform type

Speech synthesis. A collection of speech synthesis algorithms. Harmonic scans through various models including formant filtering, SAM, and LPC vowels, then goes through several banks of LPC words. The AUX output provides an unfiltered version of the underlying vocalization waveform.

Timbre:
Vocalization model

Harmonic:
Crossfade speech models

Morph:
Phoneme/word selection

Classic waves with VCF. Morphs between classic analog waveshapes which are passed through a lowpass filter. The AUX output is passed through a highpass filter.

Timbre:
Filter cutoff

Harmonic:
Filter slope/resonance

Morph:
Osc/subosc mix

Phase distortion. A dirty-sounding digital oscillator model based on 1980s digital synthesis techniques. The main outputs use phase distortion (synced carrier wave); the AUX output uses phase modulation (free-running carrier wave).

Timbre:
Distortion amount

Harmonic:
Distortion frequency

Morph:
Distortion asymmetry

Duophonic 6-Operator FM (1 of 3). Algorithms C/D/E share a common oscillator model which emulates the voice structure of the Yamaha DX7. Each of these three memory slots contains a bank of 32 DX7 sounds. Custom sound banks based on DX7 sysex files can be used, check the "User data upload" section above for instructions. Websites such as DXSysEx and Yamaha Black Boxes offer hundreds of existing DX7 sysex files for download. Use the Plaits Editor to build custom sound banks. By default, Bank C includes a variety of bass/synth sounds. For all three banks, when the Trig switch is engaged, triggers will alternate between the two voices. Modulate the FM or Pitch inputs to create chords. Leaving the Trig input unpatched results in a monophonic drone.

Timbre:
Modulation amount

Harmonic:
Preset selection

Morph:
Envelope and "time stretch"

Duophonic 6-Operator FM (2 of 3). All parameters are the same as above, except that Algo D contains a bank of 32 percussive/plucked presets.

Duophonic 6-Operator FM (3 of 3). All parameters are the same as above, except that Algo E contains a bank of 32 sustained presets (pads/strings/organ/brass).

Waveterrain Synthesis. Uses arbitrary waveforms derived from equations or image uploads, which form 2D waveshapes that resemble landforms. Use the Plaits Editor to preview and generate new waveforms. The AUX output provides a different interpretation of the terrain using phase distortion.

Timbre:
Terrain smoothing

Harmonic:
Phase shift

Morph:
Terrain offset

String machine. A four-note paraphonic emulation of classic analog string synths, including a chorus effect and stereo filter. The main output predominantly contains the odd voices (1 and 3), while the AUX output predominantly contains the even voices (2 and 4). Mix these outputs externally for an expansive stereo image.

Timbre:
Chorus/VCF

Harmonic:
Chord type

Morph:
Waveform type

Chiptune synth with arpeggiator. Generates four-note square wave chords that are reminiscent of 8-bit video game consoles from the 1980s. The AUX output generates a glitchy triangle wave that emulates the Nintendo 2A03 chip. Bonus level: enable the Trig switch and patch in a clock to arpeggiate between the notes of the selected chord.

Timbre:
Arp type / chord inversion

Harmonic:
Chord type

Morph:
Pulse width

Granular supersaw. A swarm of 8 enveloped sawtooth waves. The AUX output provides the same but with sine waves. For the classic "supersaw" sound, turn Morph fully to the right and apply subtle CV randomization to the Timbre and Harmonic inputs.

Timbre:
Grain density

Harmonic:
Frequency randomization

Morph:
Grain duration/overlap

Filtered noise. Variable-clock white noise processed by a morphing resonant filter. The tuned resonance will properly track CVs applied to the Pitch input. The AUX output uses two bandpass filters whose relationship is controlled by the Harmonic knob.

Timbre:
Clock frequency

Harmonic:
Filter morph (LP>BP>HP)

Morph:
Filter resonance

Particle noise. Dust noise processed by networks of all-pass or band-pass filters. The AUX output is the raw noise without processing.

Timbre:
Particle density

Harmonic:
Frequency randomization

Morph:
Filter type

Inharmonic strings. Similar to the "red mode" from Mutable's Rings with three voices of polyphony. This model requires an excitation signal. There are three ways to generate this signal. When the Trig input is switched off, an internal noise source will randomly trigger the exciter. If external CV is patched to the Pitch/Freq jacks, pitch changes over one semitone will also trigger the exciter. If the Trig jack is patched (and enabled with the Trig switch), the exciter will only be triggered when an external pulse is received. The AUX output is the raw excitation signal, which will be perceived as a short click or burst of noise.

Timbre:
Exciter filter/brightness

Harmonic:
(In)harmonics

Morph:
Decay time

Modal resonator. Similar to the "green mode" from Rings. Like the "Inharmonic strings" algorithm above, this algorithm also requires an excitation signal. All of the Trig and Pitch logic above also applies to this algorithm. The AUX output is the raw excitation signal.

Timbre:
Exciter filter/brightness

Harmonic:
Material selection

Morph:
Decay time

Analog bass drum. Low-frequency percussive model derived from analog hardware simulation. The AUX output provides a bass drum using an alternate DSP model.

Timbre:
Lowpass filter cutoff

Harmonic:
Envelope attack + drive

Morph:
Decay time

Analog snare drum. High-frequency percussive model derived from analog hardware simulation. The AUX output provides a snare drum using an alternate DSP model.

Timbre:
Modal morphing

Harmonic:
Harmonic/noise balance

Morph:
Decay time

Analog cymbal. Generates metallic tones derived from six square wave oscillators mixed with a noise component, routed through a VCA modeled on a low-fidelity transistor circuit. The AUX output uses three ring-modulated square waves.

Timbre:
Highpass filter cutoff

Harmonic:
Harmonic/noise balance

Morph:
Decay time

The last five algorithms in the red bank have unique responses to external triggers.

Algorithms D/E will be triggered randomly by an internal noise source if the Trig switch is off. Turn the Trig switch on to disable the noise source and switch to external triggers only. Note that with the Trig switch off and a trigger source patched in, events will be triggered by both the internal noise source and external triggers.

Algorithms F/G/H (kick/snare/cymbal) have their own tone-shaping envelope, which is controlled by the Morph knob. External triggers will activate that envelope. Turning on the Trig switch will change the Amplitude response.

The other 11 algorithms have a more direct response to triggers. With the Trig switch off, triggers will activate the envelope, opening the LPG/VCA (which is also controlled by the Amplitude knob). Turn the Trig switch on to activate the LPG/VCA. The envelope will open the LPG/VCA while the trigger will ping a simulated vactrol model. The ringing time of the vactrol model can be adjusted. Press the Trig switch and turn the Amplitude knob. From left to right, the knob will morph from a short ring time, through a more sustained and gradual decay, to a more linear VCA. This change is visualized on the upper row of LEDs.

Video Demos

Downloads

Download the latest firmware and update instructions:
1979-ao-firmware.zip