LFOs (Low Frequency Oscillators) are important tools in the world of synthesis. They are 'Low Freqeuncy' oscillators because they vibrate at frequencies that are below 20Hz – the human threshold of hearing. So why do we use oscillators that we can't hear? The simple answer is that we use them to modulate other sounds, and they can do this in a variety of interesting ways.
Most electronic producers will be familiar with LFOs, as they have become essential tools in creating synthesised bass sounds – particularly in dubstep influenced genres. In these genres, LFOs are often applied to the cut-off of a low-pass filter in order to create the infamous wobble bass sound. But there are also numerous other ways to creatively use LFOs, and we detail some of them below.
Running percussion parts through an LFO can add movement, dynamism and interest to a part that might otherwise not be that exciting. This can work particularly well on hi-hat patterns, shakers and tambourines as these are the kind of parts that are often a little lacking in character. Try using an LFO to modulate parameters such as pitch or filter cut-off, or you can even add effects like distortion to your percussion and then modify the parameters of that effect with an LFO.
There are plenty of parameters on a bass that you can modulate in addition to the filter cut-off. Play around with different parameters and figure out which are interesting to modulate over time. You can try modulating pitch or EQ settings for example; adding complexity to simple bass lines and keeping repeated patterns interesting through small variations.
You can use LFOs to automate pan controls, and therefore add side-to-side movement into your mix. The Auto Pan plug-in in Ableton uses two LFOs to perform exactly this task, and there are free plug-ins such as MSpectralPan that can do the same kind of thing. Auto-panning can be affective on synth parts, guitar solos or the kind of percussion parts we've already discussed that can sometimes benefit from some extra excitement; hi-hats, shakers, tambourines.
Using LFOs at higher depths can create dramatic effects; wobble basses being a good example of this. If you want listeners to notice a feature of your mix, then bold use of an LFO will certainly draw attention to it - but subtle changes can be interesting too. Adding LFOs with a very slow rate to a synth sound or to guitar amp settings can create subtle, evolving textures that can help to hold listener attention without hammering home the point too hard. You can even try modulating multiple parameters at different rates to create endlessly shape-shifting sounds; a useful tool in forms of music such as post-rock, IDM and ambient.
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