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)
- 16 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 (12-TET 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 the ALGO switch for a few seconds to toggle between the green 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. With the knob in the left third of its range, the pitch is not quantized. In the middle third, semitone quantization (12-TET) is applied. In the right third, octave quantization is applied. When either of the two 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.
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
Formant frequency
Frequency ratio
Formant width/shape
Row index (X-axis)
Bank selection
Column index (Y-axis)
Inversion/Transposition
Chord type
Waveform type
Species selection
Crossfade speech models
Phoneme/word selection
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, which will open the VCA. Turn the Trig switch on to activate the LPG. The envelope will open the 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. The amplifier response is visualized on the upper row of LEDs.