Algorithmic Oscillator
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
Pulse width shaper
Relative detuning ratio
Tri-saw shaper
Waveshaper waveform
Wavefolder amount
Waveform asymmetry
Modulation index
Frequency ratio
Feedback level/type
Formant frequency
Frequency ratio
Formant width/shape
Number of harmonics
Harmonic emphasis
Harmonic shapes
Row index (X-axis)
Bank selection
Column index (Y-axis)
Inversion/Transposition
Chord type
Waveform type
Vocalization model
Crossfade speech models
Phoneme/word selection
Filter cutoff
Filter slope/resonance
Osc/subosc mix
Distortion amount
Distortion frequency
Distortion asymmetry
Modulation amount
Preset selection
Envelope and "time stretch"
Terrain smoothing
Phase shift
Terrain offset
Chorus/VCF
Chord type
Waveform type
Arp type / chord inversion
Chord type
Pulse width
Grain density
Frequency randomization
Grain duration/overlap
Clock frequency
Filter morph (LP>BP>HP)
Filter resonance
Particle density
Frequency randomization
Filter type
Exciter filter/brightness
(In)harmonics
Decay time
Exciter filter/brightness
Material selection
Decay time
Lowpass filter cutoff
Envelope attack + drive
Decay time
Modal morphing
Harmonic/noise balance
Decay time
Highpass filter cutoff
Harmonic/noise balance
Decay time
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