From wobbling basslines to subtle, organic sounding sound morphing, the amount of uses an LFO has make it one of the most powerful oscillators on a synthesiser without it even making a sound. Let’s take a deeper look at how they work and how to use them…
First things first, LFO stands for Low Frequency Oscillator. Unlike the other oscillators in a synth, which operate at frequencies conducive to generating sound, an LFO typically oscillates in single digit hertz. The goal of the LFO is to create a rhythm and shape by which other parameters on a synth or sampler are modulated; most LFOs have four main functions:
Destination. An obvious one, this: you need to create a link between the LFO and whatever parameter you want it to modulate. Some of the most common are pitch and filter cutoff, but different synths have varying parameters that the LFOs can control – from envelopes to oscillator mix and phase – that will fulfill your sound design cravings.
Shape. The shape of the waveform on the LFO defines how the target parameter will move; you can imagine the shape’s up and down movements as your hand adjusting the parameter, and the rhythm with which you do it is defined by the horizontal axis, representing time. Select a sine wave and the parameter will smoothly increase and decrease through its values, select a square and it will switch between them sharply. Many LFOs have crazy, arhythmic waveforms that can be used to create natural sounding changes in a sound.
Rate. Most LFOs allow you to switch between synced and non synced rates, and each is handy for different reasons. Rhythmical effects like wobbing synths are obviously better off synced to tempo, whereas when using an LFO to create surprising and naturalistic changes to a sound, the less of a distinguishable rhythm there is the better. Changing the rate of the LFO on the fly will give you that dubstep rhythmic wobble, and sweeping the rate of an unsynced LFO that’s also set to a weird and wonderful waveform will create a totally unpredictable sound.
Amount. The amount of movement of the parameter, from minimum to maximum, will depend on this dial. Typically, the point at which the parameter you are connecting to the LFO is set is the central point, and so a sine wave will make the parameter travel the whole peak upwards and whole trough downwards from where it is physically set. Some LFO amounts will allow you to set the minimum and maximum separately for even more control. For subtle effects, like for instance simulating unstable oscillator pitch, set the amount to very low. The higher you set the amount the wilder the effect will be.
Example: Wobble Bass
The infamous wobble bass sound is created by making a synth patch that has a low pass filter in its signal. When the low pass filter is static, there is a constant ceiling above which frequencies are deadened out.
Here’s our synth with the filter sitting still:
move it, though, and a sweeping effect occurs as we become aware of that ceiling moving and the tonality of the sound changes.
Rather than sit manually twisting the cutoff knob throughout an entire song, we can ‘attach’ the cutoff to the LFO, which will modulate it for us. Using a sine wave LFO will smoothly raise and lower the cutoff by an amount we specify, so all we have to do is dial the cutoff of the low pass filter to the ‘middle’ of the sound, and adjust the LFO amount to control how wild the sweeping effect is.
Next we just set the rate of the LFO, and in this case we want to sync it to the track tempo so that we get a rhythmic wobbling sound. If we change the rate of the LFO as our bassline plays (making sure to get a healthy mix of straight timing and triplet timing to really emphasise the groove) we will be able to change our rhythm as we go!
There you have it; now you don’t just know how to get those wobbling sounds, you also know how an LFO actually works. Now you too can attract the ire of purists everywhere for using wobbling synth sounds in your productions – until they come back into fashion in six months, that is.