Next up is modulation and Operator’s LFO Shell. First off, what is an LFO? An LFO is a Low Frequency Oscillator. Lower than what? Lower than human hearing. Humans can generally hear frequencies of 20 Hz to 20 kHz (sometimes smaller ranges, for example 20 Hz to 18 kHz). So an LFO is an oscillator that oscillates lower than 20 Hz (although many LFOs can go above that into audio “audible” rates).
In synthesis, LFOs are most often used as modulation sources. To illustrate what that means, let’s look at Operator’s LFO Shell.
- The On/Off switch simply turns the LFO on and off.
- Waveform selects which type of waveform the LFO will be. *Note* – S&H stands for Sample & Hold, which creates random steps rather than a cycle.
- Range allows you to select a different range of frequencies for the LFO to operate in. Low (L) is between one cycle per 50 seconds and 30 Hz, High (H) is 8 Hz to 12 kHz, and Synced (S) allows you to sync the LFO to a time division of your current BPM.
- The Retrigger button turns LFO Retrigger on and off. With Retrigger on, the LFO will start at the beginning of the cycle every time a note is played. When turned off, the LFO will be “free running” and will start from wherever it currently is in the cycle when you trigger a note.
- Rate let’s you set the speed (frequency) of the LFO. The range of frequencies is determined by the current range parameter.
- Amount sets the intensity of the LFO.
With the same patch as we’ve been working on, turn the LFO on and copy the settings from the image above. They are:
- Waveform: Sine
- Range: L
- Retrigger: On
- Rate: 101.80
- Amount: 25%
Now check out Operator’s display window. As you can see, the LFO has envelope parameters as well. This is also where you set the LFO destination. Setting the LFO destination is basically telling Operator what parameter the LFO should modulate. By default, the LFO is set to modulate Oscillators A, B, C, and D. This would mean that it’s modulating the frequency (pitch) of each of the oscillators. This can be great for programming some effects sounds, or to add some subtle detuning movement to a sound, but for now, we are going to route it to the filter only.
In the destination section shown below, turn off all four oscillators as destinations (do this by clicking each one so that it is no longer highlighted). Then click the button labeled FIL. This turns on the filter frequency as a Mod (modulation) destination. Make sure the Destination A amount is set to 100% as well.
Then let’s use the LFO envelope to slowly bring the LFO in as the sound sustains.
Set the LFO envelope to:
- Attack: 5.79 s
- Decay: 5.89 s
- Sustain: -8.1 dB
- Release: 2.29 s
So the LFO display window should look like this now:
And it should sound something like this:
This is really just the beginning of the possibilities of modulation using the LFO. Destination B can take things to a much more complex level that we will get into later on.
For now, let’s look at the one shell we have yet to cover…