We basically need to add the controls to make our oscillator do what we want.
We have inputs from our MIDI control to control the oscillator pitch. This like an analogue synth is 1 octave pitch change per volt input.
Next comes selecting our output wave-shape so we can select different basic timbres.
After this we can have a signal modulate the phase of our oscillator to produce an interesting FM effect.
Beware: Although you could use the Pitch plug for FM it’s really not recommended as we want the modulation curve for FM to be linear, and the Pitch plug when the oscillator is used as an audio VCO is not a linear response curve.
Another useful input is Pulse Width Modulation which only affects the pulse output wave-shape. All other shapes are not affected by this voltage.
Some notes on VCO settings:
Note: You must leave the frequency scale at 1Octave/Volt! Do not change this when using the oscillator as an audio VCO.
Note: Leave the Smooth peaks option ticked unless you really want “spikey” audio.
Note: Leave the sync x-fade option checked.
Pitch control.
We want to be able to tune our oscillator(s) to a specific note or octave. For this we want the Detuner module which at a very early stage in my SynthEdit journey I modified to be a little more “musician friendly”. It’s quite a simple modification the prefab control’s structure is shown below. All that’s needed is to click on the “Tune” switch module, and then alter the choices in the properties panel on the right to read the same as I have in mine. You now have a note choice that reads C, C#, D…etc. instead of 1,2,3,4. Now you no longer need to remember that 4 = Eb.
The octave switch we can leave “as is”, likewise you don’t need to touch the values on the fine tune control.
Pulse width.
Before connecting anything to the Pulse Width plug change it’s default value to 0 in properties. Next connect the plug to the IO Mod, and connect a slider control to it with a minimum of -8 V and a Maximum of 8 V. This will give the widest useful range of pulse width, with 0 V corresponding to a square wave.
Phase Modulation
Leave the Phase Mod plug at the default value of 0V, and connect it to the IO Mod.
Change the PM depth from 5 V to 0V, and connect the IO Mod to the plug, and a slider control. You can leave this with its default Minimum and Maximum values.
We can use this to connect to the output of another VCO if required to create an FM effect on the waveform.
Sync.
This can be used to synchronize this oscillator to another oscillator, effectively locking the two together to produce further changes to the tone of the audio output. By Using Sync we could have a master oscillator, and synchronize say another three (slave) oscillators to the Master, enabling us to create a wider range of timbres by selecting differing octaves, and pitches for the oscillators (their pitches will be synchronized, but the resulting wave-shapes will be altered). This master/slave oscillator setup was used in Moog Modulars with great effect.
The finished oscillator.
Now you have an oscillator which will track the pitch(es) played on your midi keyboard, and can be modulated in some useful ways. It can be synchronized with or to other oscillators. We also have a choice of Sine wave, Sawtooth, Ramp, Triangle, Pulse, White noise and Pink noise audio outputs.
Leave a Reply