Along with my top 5 music mixing tips, one of the most important things you can do with every mix is keep it dynamic. I’m not talking about it in the compression sense, I’m talking about the general sense and vibe of the mix itself. Your mix should always be evolving to keep the listener engaged. An easy way to keep your mix lively is by utilizing LFOs. Let’s define what is an LFO and how you can use it to keep your mix from stagnating.
What is an LFO
LFO stands for “Low Frequency Oscillator”.
I recently talked about oscillators (see what is an oscillator in music) which are electronic devices which create single cycle wave forms which operate at high frequencies, producing sound. They are the basis of wavetable synthesizers both analog and digital (virtual instruments like Serum) and allow you to create all kinds of basic wave shapes and sounds.
The difference with an LFO is that “low frequency” part. The oscillator is generating waveforms at subsonic speeds of typically 20Hz or less. Thinking back to the four parts of a sound wave, 20Hz means that the wave length cycles/repeats 20 times per second.
That may still seem fast, but it’s happening so slowly that we can’t hear it, hence the term subsonic.
What good is a sound wave when it’s operating at subsonic speeds and frequencies?
Synthesizers, effects processors, and samplers can all apply LFOs to various parameters of your audio to modulate them, meaning changing them over time.
In other words, an LFO modifies existing sounds in interesting and evolving ways.
How to Use an LFO
Modulation comes in many forms which you can apply to any type of track or instrument in your mix.
Routing these ultra low frequencies to different parameters yields different results.
For example, routing an LFO to modulate a sound wave’s amplitude creates a tremolo effect which I’ll talk about in a moment.
Routing an LFO to the pitch of a sound wave creates a vibrato effect. We can route an LFO to a high or low pass filter to get a warble or rippling effect, respectively.
Sometimes modulating multiple parameters at once creates the basis for effects we’re already familiar with.
I covered the more popular options in my audio effects explained overview, but some of these include:
Chorus is a good place to start when talking about how an LFO works. You’ve likely used this effect on occasion, possibly without realizing (or caring) the mechanics behind it, but this effect utilizes an LFO to operate.
Chorus creates duplicate instances of your sound that you’re applying it to, then it uses a low frequency oscillator to change the pitch and timing of those duplicates over time. This creates the illusion of distinct copies of the original audio and provides a lush thickness when played over top of the original.
The slow vibration of the low frequency oscillator going through the pitch and timing is what makes this evolving change possible. Here I explained how the “Rate” feature (which is a standard feature on most chorus plugins) on the Arturia Jun-6 Chorus plugin works:
I go into more detail in my overview of what is chorus, but this effect works particularly well on vocals and guitar to bring out some subtle added thickness and width when necessary.
With the right settings like I show above, you can create a large and lush tone to bath your audio in which is that classic tone we think of when we think of chorus.
Whereas a chorus effect uses an LFO to modulate time and pitch slightly, a phaser utilizes an LFO to modulate peaks and troughs through the frequency spectrum.
The result is a smooth evolution between favoring higher and lower frequencies in alternating fashion.
If you speed up a phaser you get a choppy effect where the audio itself sounds faster.
Slowed down, a phaser produces a washy pleasing effect over your audio.
Phasers in particular are popularly used on guitar, and phaser effects pedals are some of the best selling modulators for the guitar.
You can apply a phaser to individual tracks, buses, or even the master bus here and there in your mix to achieve a number of interesting aesthetic effects to keep your mix fresh, contrasting a short phaser heavy bridge section before stripping it away for a clean (and big) final chorus.
Let’s leave pitch alone for a moment. What if we want to modulate the amplitude of the sound wave?
Tremolo uses an LFO to modulate the volume of your audio up and down, in and out. You can really slow it down to create a smooth transition between no and full volume, or you can speed it up to create a choppy in and out break, even matching it to the BPM of your song.
You might not know tremolo by name but everyone knows it by sound when you give a famous example like the opening guitar effect on Green Day’s “Boulevard of Broken Dreams”:
A flanger creates a duplicate of your signal and delays it slightly while varying the timing via an LFO.
You’re probably thinking that sounds an awful lot like a chorus, and you’d be right.
Typically with a flanger we’re dealing with much shorter delays. As the signals go in and out of phase you get a comb filtering effect (by choice of course).
A practical example of the use of a flanger is on the drums at the start of Blink 182’s “Feeling This”.
The flanger gives them an evolving and distant sound until they come in harder as the effect is removed for the verse.
In opening I mentioned that LFOs can help keep your mix dynamic. The evolving effect they have can give the audio in your mix the feeling of being alive.
Even better is that opposed to a more laborious technique like volume automation, this is a relatively low maintenance way to introduce dynamic elements into your mix to keep it fresh for your listener.
The use of LFOs gives a track or tracks in your mix that extra bit of life to keep your mix evolving and your listener engaged, so think about introducing more of these elements in your next mix.