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!

Enjoying Envelopes


We find ourselves once again sauntering through the summer of synths. Last time, we went over the tone sculpting power of filters and how we can use them to let through and/or block low sounds, high sounds, or both.

In addition to filters, we’ve figure out how make pitches using oscillators and how to adjust the primary sonic nature of said oscillators by using different waveforms.

Now we need to harness the actual execution of our pitches. At the moment (presuming we’re using a keyboard to make notes occur), when we strike a key, the note instantaneously starts, remains the same while we hold it, and then immediately stops when we let go. A nice start, but we can go so much further with the power of envelopes!

Before we get into what envelopes are in the synthesis world, I want to say you have to dig pretty deep in the dictionary to find an appropriate definition of the word.

We’re certainly not dealing with items made to contain letters, but we’re also not dealing with many of the other definitions. In fact, I had to go down to the sixth definition to find something even close to what we’ll be discussing today.

Just so we have it, said definition was: “Electronics: a curve joining the successive peaks of a modulated wave.” Not the most enlightening definition in the world, so we’ll focus on four easy letters instead:

A. D. S. R.

These four letters stand for Attack, Decay, Sustain, and Release, and they are the building blocks of any synthesizer envelope. To get a better idea of what each of these words mean, let’s put them into a visual format:


Each line goes along with one of the letters. The first rising line is Attack, the next falling line is Decay, the flat line is Sustain, and the final falling line is Release. Moving left to right on this picture represents moving forward in time, while moving up and down represents how “strong” the envelope is (this “strength” can represent volume, brightness of tone, etc.).

The Minimoog Voyager has two envelopes: the volume envelope and the filter envelope. We’ll discuss volume first as I think it’s easier to wrap one’s head around.

The volume envelope determines how long it will take for a note to begin after striking a key (attack), if the note will fade a bit (decay), how loudly the note will ring out (sustain), and how long the note will fade after releasing the key (release).

If you have a very short attack, the note will begin instantly, which is similar to plucking a guitar string. If you have a very long attack, the note will slowly fade in, which is similar to a slowly pulling a bow over a violin string. The Moog can have an attack of 0 seconds all the way up to 10 seconds!

After the initial attack, the note might Decay to a lower volume. Going back to the guitar, the initial pluck is quite loud, but the sound of the string ringing out afterwards is generally softer. The time it takes to get to that softer ringing out is our Decay length. Just like Attack, this can be 0-10 seconds in length.

Once the Decay has occurred, the note will continue to Sustain as long as the key is held. So the value of the Sustain knob is not about time (unlike Attack and Decay). Instead the Sustain knob dictates how loud the sound will be after the first two stages of the envelope. If the Sustain knob is all the way down, the sound will fade away to nothing after the Attack and/or Decay. If the Sustain knob is all the way up, the sound will never Decay at all and will remain at full strength after the initial Attack.

Lastly, we have the Release. This is the amount of time it will take the sound to fade away once you release the key. Once again, we have a large range of options given that the release can last 0-10 seconds. You may want the sound to cut off instantly, you may want a bit of a taper, or maybe you want some epic, trippy space sounds that seemingly last forever.

To better demonstrate all of this, here’s a video exclusively on the Volume Envelope.

Right next door to the Volume Envelope is the Filter Envelope.

The same picture from above applies, but this time, going up and down on the picture represents how open or closed the filter is (if you missed the last post on Filters, I highly recommend checking that out first before proceeding).

A. D. S. and R. all work exactly the same as on the Volume Envelope. We’re just choosing how quickly to open and close the filter. The Sustain decides how open or closed the filter will wind up after the initial Attack and Decay, and the Release will fully close the filter over a certain amount of time.

Side-note: the Volume and Filter envelopes are independent of each other, so you could have two radically different envelopes going on at the same time, which enables you to create some wonderfully unique sounds.

The only unique item on the Filter Envelope is the knob called “Amount to Filter.” Unlike most knobs that proceed clockwise from least to most, this knob is “off” at the 12 o’clock position. When turned to the right, it has a positive effect on the envelope, and when turned to the left, it has a negative effect on the envelope.

When in positive mode, the envelope matches the picture above. The filter starts off closed and opens as it increases in strength.

However, when in negative mode, the envelope becomes a mirror image (flipped upside down) of the picture above. The filter starts open and closes as it follows the Attack, the Decay opens it back up, etc.

Once again, a video will do wonders to make all of this clearer.

One other item in the Envelope section that wasn’t touched upon today was the Envelope Gate. We’ll cover gates in a later post and will come back to this. For now, this post is under the presumption that all notes are activated via a keyboard.

With that all said, we’ve covered the main components of making sound on a synthesizer! Next time, we’ll get into how we can start to really modify and tweak our sounds via the LFO (Low Frequency Oscillator) and Modulation Busses. Things are about to get wild!