Intro to Synthesis, Part 5: How to Use Amp Envelopes and Filter Envelopes

Our new, six-part Intro To Synthesis series is made for novices first getting into synthesizers, as well as seasoned synth heads hoping to better understand the core concepts at the foundation of their instruments. So far, Reverb’s Justin DeLay has covered the basics of oscillators, how filters add shape and character to a synth’s tone, and, just last week, how to use an envelope’s parameters.

Today, in the series’ penultimate video, we dive deeper into envelopes. We’ll be defining the differences between envelopes, how an envelope’s settings affect your volume and filter, and specific techniques for using envelopes to change the response, timbre, or even the pitch of a given note.

A critical lesson here are that there are different kinds of envelopes, each with similar parameters but distinct functions.

The amp envelope, by affecting your synth’s internal amplifier, will control the volume. The Attack parameter here will determine whether your note will come in immediately or gradually, while the Decay and Sustain knobs will set how present the sound will continue to be after the initial hit. The Release will determine how quickly or slowly the sound expires after your release the key.

"If you’re trying to get a really clicky, percussive sound, turn your decay all the way down so that essentially the envelope closes right away, with zero sustain," Justin says. "And these are super fun if you have an arpeggiator or a sequencer or if you’re sending MIDI to your synth to get a repeating pattern going." By changing the Decay, Attack, Release, or Sustain while an arpeggiated pattern plays, you can continuously evolve the sound.

If you’re trying to get a really clicky, percussive sound, turn your decay all the way down so that essentially the envelope closes right away, with zero sustain."

An amp envelope can be also be a versatile tone-shaping tool all by itself. As Justin demonstrates at the beginning of the video above, it can be used to create a reverse effect—if you set a slow attack and immediate release, which is the opposite of the naturally quick attack and slow release common to instruments like guitars.

You can also "defeat" your amp envelope so that the volume remains constant throughout the life of a note, with no attack, full decay, full sustain, and no release. This will give you a pure, on/off sound that’s good for synth basslines.

These same concepts apply to the filter envelope—except, instead of modulating the amplifier’s volume, these envelopes will modulate your synth’s filter and the cutoff frequency of your sound. And the full shape of a synth’s sound will be found through a combination of your amp and filter envelopes.

There will likely be a knob in your filter envelope section that will be called "Envelope" or, as it’s written on Justin’s Korg Mono/Poly, "EG Intensity," that will determine how much the envelope is modulating the filter. It’s important to note that this Envelope setting will add to the maximum setting of your filter—if you set your filter at 2 and set this Envelope knob to 3, then you’ve given the filter a new maximum setting of 5.

Korg Mono/Poly Analog Synthesizer

Dialing in a combination of parameters from the amp envelope and the filter envelope will ultimately determine to timbre and shape your sound. If, for example, you have the amp envelope set to a quick attack, and the filter envelope set at a slow attack, you’ll have a tone that starts immediately but gets brighter over time.

As Justin says, if you want a sound with a longer release, it can sound pleasing to the ear if your filter envelope is set shorter than the amp envelope’s. This will let you hear the full filter sweep down before the volume dies. You can even use the filter envelope to change the pitch of your sound or to introduce pulse-width modulation, or changes in the shape a square wave.

Check back next week for the final episode of this season of Intro To Synthesis, and be sure to get all caught up by watching all of the previous videos below.

More Intro To Synthesis Videos
Intro To Synthesis Part 1 and 2: Oscillators
Intro to Synthesis Part 3: What's A Filter?
Intro to Synthesis Part 4: How to Use an Envelope’s Attack, Decay, Sustain, and Release

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