The Lovely LFO

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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!

Oscillation of Oscillators

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Salutations synth seekers! Last time, we discussed a brief history and overview of analog synthesis.

Additionally, I left everyone with two major points that will act as the bedrock for all topics moving forward:

1. Everything is made of waves.
2. Anything can be a source OR a destination.

While that’s all well, swell, and good, it won’t help us at all until we have some basic sounds to work with.

To do so, we should briefly discuss the nature of sound. Most of us learned in school about how sound is made of vibrations in the air and our ears picking up on those vibrations via changes in air pressure.

One term that I’ve noticed doesn’t get used as often is oscillation. An oscillation is a movement back and forth at a regular interval. In sound, those oscillations are the vibrations that we just mentioned. It could be the oscillation of a guitar string vibrating back and forth after being strummed; it could be the oscillation of a drum head after being struck by a stick; it could be the oscillation of your own vocal chords when you sing your personal tribute to the glory of synthesizers.

In an analog synthesizer, we will always find at least one oscillator as the catalyst for creating basic pitches. Many synthesizers have two or three oscillators, so you can create chords (multiple pitches sounding at the same time) or use those oscillators as other sources for modulation (this will be covered later on).

These oscillators have a voltage that is translated to a certain pitch. The higher the voltage, the higher the pitch and vice versa.

Some synthesizers, like my Minimoog Voyager pictured at the top of this page, can actually generate such a low voltage that the pitch becomes subsonic – meaning that human ears can’t perceive it. I’ll use this concept later on to demonstrate how the increasing oscillations lead to higher (and perceivable pitches), but I believe I can provide a more clear example using a metronome app.

The metronome on my phone far exceeds what most metronomes can do, and one of those items is that it can click so quickly that it winds up generating a pitch.

Imagine that as I increase the speed of the metronome, I’m really increasing the voltage of an oscillator on a synth.

You’ll notice that the clicks became so fast, they essentially “blurred” into a perceivable note. The same thing happens as we move from the subsonic to the sonic, but unless you’re a superhuman with super ears, an audio example of that wouldn’t carry the same meaning.

To put the velocity of this blurred speed into perspective, middle C (the note most of us learn first in the world of piano) vibrates about 261 times every second. That would be the same as hearing 261 of those clicks on that metronome app in a single second!

Lastly, regarding most synths, the oscillators have a few parameters that can be modified to change the sound:

1. Frequency
2. Octave
3. Waveform

The frequency is often a knob that allows you to shift the pitch up or down by a certain amount of steps (C to C# to D to D#, etc.). On my Moog, you can shift up or down each oscillator by a sixth (C to A as an example).

This can be used to generate chords, create a detuned (out of tune) sound, or many other items that will come into play in the coming weeks.

However, if you want to explore a larger range of pitches, you can incorporate the octave knob. This allows you to quickly jump a octave (C to C up or down) or more with a single action.

The range of octaves varies from synth to synth. Moog has always loved to push the envelope in this regard, so the Voyager can go through six octaves per oscillators. They are marked: 32′ 16′ 8′ 4′ 2′ 1′.

These marks are in reference to the pipes of a pipe organ. If you start with a pitch from a gigantic 32 foot pipe and cut it in half, you’ll get a pitch that’s twice as high (one octave) through a pipe that’s half as long. This process continues all the way to a one foot pipe.

Now that we’ve established what oscillators are, how they work, and how to get different pitches from them, we arrive at the waveform knob. This is a much deeper concept than just adjusting the frequency or octave, so it will be the topic of discussion next time.

Hopefully, you feel a bit more clear on the general idea of oscillation and how that concept has led to oscillators being the main generators of pitch in the synthesis world!