An LFO is a low-frequency oscillator that is used to modulate a synthesizer controls automatically, and in a regular fashion. They are often used to modulate the filter cut-off frequency at a slow rate, for vibrato and for tremolo effects. Though it’s almost identical to an oscillator that produces audible waveforms, its frequency lies in the subsonic range between 10 Hz and 0.001 Hz. The most common waveforms are sine and triangle as shown below.
We can use the standard oscillator module to create an
LFO in SynthEdit.
Click on the module, and in the oscillator’s Properties window you will
see two modes for setting the frequency;
1 Volt/Octave,
1 Volt/kHz.
I recommend using 1V/kHz as it’s easier to work out your frequency ranges.
Since 1V = 1kHz, then 0.001V = 0.001kHz or 1Hz. It’s easier to work out 1 volt per kHz values, than using the 1 volt per octave formula below (unless you enjoy maths).
How low can you go? The stock SE Oscillator will (Since an update in 2019) go down as low in frequency as -1e27 kHz (0.00000000000000000001 kHz)… that’s well below 0.01 Hz.
An oscillator’s default output range is +5 to −5 volts. By adding a Level Adj
module in after the oscillator’s Audio Out plug you can adjust the
LFO’s output amplitude.
Note: If you make the range of the Level knob -10 V low to 10 V high, then when the Input 2 voltage is negative it will invert the phase of the waveform, and when it is positive the waveform will be in it’s normal phase.
Using the LFO is as simple as connecting to the Pitch plug of a filter (NB there are some filters such as the Butterworth EQ range that should not be modulated), the Pitch plug of an Oscillator (only small amounts are needed here) or the Volume plug of a VCA (it’s better to use a VCA than a Level Adj module).
By default this LFO will be “monophonic” this is because it is not connected to the MIDI-CV converter module. However we really don’t need to have a polyphonic LFO (and it would be a waste of valuable CPU resources too).
If you decided you really needed a polyphonic LFO, then you could connect the Phase Mod plug to the Pitch plug of the MIDI to CV module, and set the PM depth level to 0.
This is OK if you don’t mind having a few options an LFO wouldn’t normally have such as Pink/White noise. There is however a couple of excellent 3rd party LFO modules from TD modules which give you lots of extra options, see the TD LFO modules post.
We can also have even more complex modulation possibilities with a “complex LFO” by having a number of LFOs modulating each other.
Leave a Reply