The Lovely LFO


Greetings once again feller synthesis seekers! As the Summer of Synths comes to an end and as we look ahead to the Fall of Filters (which really isn’t the case since I already did a post on filters, but one must embrace the power of alliteration), we’ll wrap up August with a short post on LFO’s.

The big reason for the brief post is threefold: first, my wife and I were totally absorbed by the Rio Olympics; second, preparing for the school year (new schedule for my piano students, getting my entire year set up with the bands/orchestras/choirs I accompany, etc.); lastly (and most important to you, the reader), Lindby has a lot of new content on the horizon.

In fact, to accommodate this new content, Master Claset’s Theory Corner and Synth You Asked will now be posting once a month rather than every other week. If you want to be totally up to date on all these new Lindby endeavors, make sure to subscribe to our monthly mailing list by going to our homepage and scrolling down to the bottom! With that said, let’s return to LFO’s.

LFO stands for Low Frequency Oscillator. It functions just like the oscillators we discussed in the second ever Synth You Asked post. (I’d definitely recommend checking it out before reading the rest of this post!) The main difference is that the LFO is very slow and thus at a very low frequency. In fact, they’re so slow and low that we can’t even hear them!

Because of this, the LFO isn’t used for the sake of generating pitches. It’s used as a means of modifying and modulating aspects of the sound: pitch, waveform, filter settings, etc. This is accomplished via two main waveforms: a triangle wave and a square wave. The triangle makes the changes nice and smooth while the square wave is direct and instantaneous.

For the LFO section of the Minimoog Voyager, there are only two parameters to consider: LFO Rate and LFO Sync.

LFO Rate refers to how fast or slow the oscillations occur. It ranges from 0.2 Hz (one oscillation every five seconds) up to 50 Hz (50 oscillations every second). Since the human hearing range does go down to 20 Hz, we could technically hear the very high end of an LFO, but it’s hardly practical given what the main oscillators can do.

The LFO Sync provides four (technically five) methods to start/restart the oscillation process. They are as follows:

Off/Sync: The LFO runs independently unless something is plugged into the LFO Sync jack on the back of the Minimoog Voyager (this will be covered at later time).

MIDI: The LFO can be controlled via MIDI signals (once again, this will be a topic to discuss later with MIDI in general).

KB (Keyboard): The LFO resets whenever a new note is played on the keyboard. This can be useful when you want a new pitch to correspond to what the LFO is doing.

ENV. GATE: This will allow the LFO to be reset via an external gate plugged into the Envelope Gate Source jack (like Sync, this will be covered when we discuss physical inputs/outputs).

Lastly, the LFO plays an integral role in the S&H circuit (Sample & Hold), but I’d like to save that for the next post where we discuss Modulation Busses and the wealth of options entailed there.

As always, here’s a video that properly demonstrates everything discussed above.

We’re closing in on having covered all the basics. Next time, we’ll harness all of these ideas and put them to work!