Basics of Synthesis: LFOs

G’day! Tom here from Island Studios. Welcome back! If you haven’t checked out my last couple of tutorials on waveforms and envelopes, I’d recommend doing so before you dive into this one - but if you’re just keen to learn about LFOs, feel free to continue anyway!

What Is An LFO?

A vital yet often overlooked ingredient in creating a great synth sound is an LFO, or Low Frequency Oscillator. This is used to add modulation to a sound, and could be assigned to anything - pitch, volume, filter cut-off frequency… depending on your synth, the list could be endless.

The LFO process is quite self-explanatory: we apply a (usually) slow warble to a parameter of our choice. A great example of this is vibrato - think of a vibrato pedal, and how it slowly and steadily modulates the pitch of the source audio. This is really just an LFO applied to the pitch. With most LFOs, you have the ability to control the rate and the depth.

LFO Rate

The rate determines how quickly the oscillator is completing one cycle of modulation. The maximum speed tends to be relatively slow - hence the words ‘low frequency’ in ‘low frequency oscillator’ - although many modern LFOs do have a higher maximum speed than you might expect. If you can’t find the rate parameter in your synthesiser, perhaps look for a parameter that says ‘speed’ or ‘frequency’.

LFO Depth

Meanwhile, the depth determines the intensity of the modulation. For example, do we want to modulate the pitch of our sound by three octaves, or do we want to modulate the pitch of the sound by 12 cents? On some synthesizers, the depth parameter might be described as ‘amp’ or ‘strength’, so look closely.

Using LFOs in Your Music

Now, let’s have a go at applying an LFO ourselves. My synthesizer of choice is Massive, but most modern software synths should have an LFO with the same parameters as the ones we’re talking about here. Let’s apply an LFO to the pitch of whatever synth sound you’ve built - perhaps to the pad sound you built at the end of the Basics of Synthesis: Envelopes tutorial (just make sure you have a high sustain value).

Depending on your synthesiser, the process of applying an LFO may be a matter of dragging and dropping, or clicking a drop down menu, or something else. I recommend doing a bit of research to see how you apply an LFO specifically using your synthesizer.

Assigning an LFO in Massive by Native Instruments

In Massive, you should drag your green LFO tab over to the oscillator section, and drop it into the top blank square beneath your ‘pitch’ parameter (see left). Click on the number that appears in the box, and drag upwards until you reach 12 semitones… for now. Then, click over to the green “5 LFO” section, and max out the depth and rate parameters so you can hear the modulation.

It’s probably sounding a little bit chaotic at the moment, but bear with me. We’ll start by finding a more appropriate rate. Some rate parameters will not have an observable frequency value, in that case, use your ears! Once you find it, slowly start bringing it down until you’re sitting at about one full cycle over the course of 2-3 seconds. This is a nice speed for a subtle vibrato. However, there is likely nothing subtle about what you’re listening to right now - so let’s drop that depth down. As you can see in the above figure, the Depth parameter is labeled as ‘amp’, which I assume means amplification (I find that an odd choice of word, but we’ll carry on). Drop the depth right down until you have a nice subtle vibrato - it should be very close to the minimum setting on the knob.

Refining The Modulation

The method I’ve just described is fast…however perhaps not as malleable or tweakable as you might like. To address this, most synthesizers allow you to set a maximum modulation range. Remember earlier how we bumped that number underneath our oscillator’s ‘pitch’ parameter up to 12 semitones? Let’s drop that down to a few cents. I recommend around 0.13 semitones, which always sounds quite nice to me when working on a pad sound. By doing this, we’re telling the synth that it cannot modulate the pitch by more than 13 cents - which allows us to max out our depth/amp parameter. Now we have much finer control over how much modulation we want to occur. We could apply this technique to all sorts of modulation types - for example, a maximum filter frequency for the LFO to modulate open and closed.

Advanced LFO Techniques

LFO utilisation can get very complex very quickly, but I’ll briefly discuss a couple of more advanced techniques/components you can apply in your synth production. The first one is using an LFO to modulate an LFO. For example, you might want the rate of your LFO to be modulated by another LFO - speeding it up and slowing it down throughout one whole cycle. Most modern synths will allow you to drop an LFO onto the rate of another LFO, allowing you to easily achieve this. Of course, you could stack as many as possible… you might want an LFO to modulate the depth of the LFO that is modulating the rate of your first LFO. Yeah. It’s a lot. Experiment!

Another more advanced component is the use of waveforms when tweaking your LFOs. As you can see in the above figure, you can choose other waveforms to carry your modulation. The default selection is usually a sine wave, but if you want a super sharp and aggressive LFO, you might select a square wave. This, for example, will jolt between the minimum and maximum values that you have set. If you need a refresher on waveforms, head back and check out my tutorial Basics of Synthesis: Waveforms to suss out how different waveforms work, and what they look and sound like.

Anyway, I could go on forever. The world of Low Frequency Oscillation is a fantastic world. Practice using LFOs, and see what cool parameters you can modulate - you can get some super unique and wacky sounds. Until next time, thank you!