Intro to Synthesis, Part 4: How to Use an Envelope's Attack, Decay, Sustain, and Release

Our new, six-part Intro To Synthesis series promises to guide anyone interested in synths through the essentials of the instruments. We began with two videos that explain the basics of oscillators—the sound generators that serve as the foundation of a synthesizer’s tone. Last week, we explored how filters add shape and character to a synth’s tone.

Today, we turn our attention to envelopes and their most basic tone-shaping features.

Reverb’s resident synth head Justin DeLay begins by defining just what an envelope is—"a control signal over time" that determines "how quickly or slowly you’ll close the filter." As a note from an acoustic instrument behaves differently depending on how you hit, pluck, or bow it, synthesizers use envelopes to change how a sound develops over time.

Envelopes generally have four parts that help to determine this response. The attack knob will determine whether a struck note or chord is immediate—like a drum—or gradual, as a bowed violin. While the attack is the upward measure of how loud a sound gets over time, the span class="weight-bold">decay is the downward measure of how loud a sound gets over time, as it falls back from its peak.

Like with an attack setting, a decay knob can be adjusted to have a long or short decay. "But what level of volume are you eventually decaying down to?" Justin asks. That’s the sustain—"the relative volume of your sound after the attack and decay portion have finished."

Having no sustain means that the sound will immediately cease after the decay, while a low sustain setting will let the sound settle into a quiet, final volume. The release function determines if the sound quickly stops after the sustain portion, like an organ—which stops as soon as you take your hands off the keys— or if will have a "graceful transition from note to note" and eventual silence.

As Justin demonstrates, with a high release setting, you can have a smooth, flowing sound even if you’re playing the keyboard in a staccato fashion.

While these are the very basics of envelopes, next week Justin will explore the great, unique sounds and almost limitless tone-shaping possibilities envelopes and amp filters have to offer. So be sure to watch the latest video above, but also be sure to check back next.

Full Intro to Synthesis Series
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