Harmonic Oscillator

You can get the schematics PDF here.

This is a fully featured, wide range, voltage controlled oscillator with simultaneous dynamic control over pitch, timbre (harmonic content) and amplitude.

The Harmonic Oscillator module (OSC HRM) is used to create pitched waveforms with dynamically controlled timbres. Pitch control law is 1V/Oct and the module uses a platinum element for temperature stabilization of the pitch curve. The scale is perfectly tuned in the middle six octaves up to a pitch of 4.000 Hz. With external cv the pitch range is 18 octaves.

When playing pitches higher as 4000 Hz the 1V/Oct scale starts to break down, due to the necessary internal band limiting in the harmonic generators. The switch has three positions, in the upward position the pitch knob can tune the osc between +/- 0.5Hz and 25kHz, so over the full range. In the middle position the pitch knob is disconnected and the osc tunes to middle C, so it can be easily played by a 1V/Oct MIDI CV without the possible chance of severely detuning the osc by accidentally twisting the pitch knob. The fine knob still works, of course. The third position tunes the osc an octave below middle C.

The Fine knob curse is about two half notes up and two half notes down. It is limited for the reason that it should be able to precisely set the detune between two oscillators. To make a detune of e.g. a fifth it is more interesting to use the quantizer from the NodeProcs, as this module can add the correct voltage to e.g. a 1V/Oct signal for transposing a particular note interval, up to five octaves up or down and optionally quantized to a chosen scale.

The Chain Out jack is like a multiple when chaining two or more oscs to one 1V/Oct signal. It is handy when e.g a MIDI->CV box or analog keyboard has only one 1V/Oct jack, in which case a cable is connected between the first osc chain output and the second osc 1V/Oct input.

The module uses a biquad sine/cosine oscillator at its core and through a process of recursion harmonic series of overtones are generated. There are two recursion paths, one that produces all harmonics and one that produces only the odd harmonics. Odd and all harmonics can be controlled with CV. Dynamic wave shaping is available through the ODD HRM & ALL HRM controls. By gradually opening the knobs that control the amount of recursion more and more harmonics are generated.

The first circuit adds odd harmonics, which lets you morph the sine wave into a square wave, but with a somewhat different response than what you would get just by using a filter. The second circuit adds all harmonics, modulating between a down-saw, through a sine, to an up-saw. Or actually, the center position could be a sine, or a square wave, or something in between. The center position is basically whatever the first circuit is currently doing to the waveform. The HRM MOD CV input has an attenuator. PWM can be created by turning up the odd harmonics and change the all harmonics. Building up these harmonic series is under full voltage control and can be modulated from slow LFO speeds to fast audio rates to create FM timbres.

When the waveforms are modulated there is a negligable amount of detune (less than 1 cent), though when modulating at audio rates an asymmetry in the modulating waveform can cause detune effects on deep modulations. ODD HRM morphs the Sine output to a Square wave under manual and voltage control (without attenuation).

ALL HRM morphs from Inverted Saw (manual control fully anti clockwise) through to Sine (manual control set to noon) to Saw (manual control fully clockwise). The HRM MOD CV input has an attenuator. The signal starts as a sine wave, which then gets modulated by two separate voltage-controlled analog waveshaping circuits to create a wide variety of waveforms and sounds. The first circuit adds odd harmonics, which lets you morph the sine wave into a square wave, but with a somewhat different response than what you would get just by using a filter. The second circuit adds all harmonics, modulating between a down-saw, through a sine, to an up-saw. Or actually, the center position could be a sine, or a square wave, or something in between. The center position is basically whatever the first circuit is currently doing to the waveform. The waveforms have an exceptionally warm sound and when dynamically modulated have a deep spatial and organic character.

This arrangement lets you do all sorts of filter-y effects without using a filter, or you can create a big fat mixed square+saw wave, or you can create a waveform with a very animated timbre that sounds somewhat saw-ish, but that has a really strong sweeping effect imparted on the saw wave that sounds kinda like flanging or pulse width modulation.

There is an additional VCA incorporated in the module with manual initial gain control and an attenuated CV input. This is useful for manipulating FM levels. Having a VCA at the end of the signal chain does not affect timbre, this arrangement does allow timbre changes, as well as ring modulation type sounds. It can be used simply to control the level, like other VCAs, or you can patch the VCA out to one of the harmonic modulation inputs to make the module’s waveform modulate itself under control of the VCA. One can control the velocity parameter with MIDI. The advantage is that sometimes effects like distortion are depending on loudness. VCA output and direct oscillator output (Full out) are doubled for convenient patching to two destinations (i.e. to have two separate signal paths sourcing from one oscillator). The final output signal can be taken from a point just before the VCA and at the output of the VCA. This enables the module to be easily used in a situation where one wants to modulate another module by an audio rate signal and have the modulation depth under voltage control using e.g. a LFO waveform, an envelope voltage signal or a play controller that produces a control voltage, while still having the full output level signal available on the full output to serve different purposes.

With only one OSC HRM and one DUAL ENV module you can already have a voice with dynamic timbral and volume control that can do e.g. a pretty solid bass line.

There is now an addition of a Sub Out to the OscHRM that do not change any of the existing functions of the OscHRM. This suboctave is a pulse one octave below the osc that inherits its pulsewidth from the EVEN and ODD settings and modulations. Also the output level is controlled by the VCA LVL and VCA MOD knobs and input signals. It replaces one of the VCA OUT connectors, so from now on there will be one VCA OUT and one SUB OUT, both controlled by the same level and waveshaping settings.

Older information (redundant):

The Harmonic Oscillator module (OSC HRM) is used to create pitched waveforms with dynamically controlled timbres. Pitch control law is 1V/Oct and the module uses a platinum element for temperature stabilization of the pitch curve. Maximum frequency range is from 0.5 Hz to 16.000 Hz and the scale is perfectly tuned in the middle six octaves up to a pitch of 4.000 Hz.

When playing pitches higher as 4000 Hz the 1V/Oct scale starts to break down, due to the necessary internal bandlimiting in the harmonic generators.

The module uses a biquad sine/cosine oscillator at its core and through a process of recursion harmonic series of overtones are generated. There are two recursion paths, one that produces all harmonics and one that produces only the odd harmonics. By gradually opening the knobs that control the amount of recursion more and more harmonics are generated. When only the all harmonics path is used the waveform morphs smoothly from a sinewave to a waveform that closely resembles and sounds like a sawtooth or an inverted sawtooth. Opening only the odd harmonics knob will smoothly morph from a sinewave to a squarewave. When opening both knobs effects like pulse wave modulation are possible. Building up these harmonic series is under full voltage control and can be modulated from slow LFO speeds to fast audio rates to create FM timbres.

When the waveforms are modulated there is a negligable amount of detune (less than 1 cent), though when modulating at audio rates an asymmetry in the modulating waveform can cause detune effects on deep modulations.

There is an additional VCA incorporated in the module. The final output signal can be taken from a point just before the VCA and at the output of the VCA. This enables the module to be easily used in a situation where one wants to modulate another module by an audio rate signal and have the modulation depth under voltage control using e.g. a LFO waveform, an envelope voltage signal or a play controller that produces a control voltage, while still having the full output level signal available on the full output to serve different purposes.

The waveforms have an exceptionally warm sound and when dynamically modulated have a deep spatial and organic character. With only one OSC HRM and one DUAL ENV module you can already have a voice with dynamic timbral and volume control that can do e.g. a pretty solid bass line

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