Natural sounds change over time. One of the most common ways to emulate this phenomenon is to use an envelope, a control signal that modulates a synthesizer parameter or signal over time. They come in various shapes and sizes, with the ADSR envelope being the most popular type. They can and are used to control everything from amplitude to frequency to the index of an FM modulator to the shape of a grain, etc. The envelope is a synthesis fundamental.
In today’s example, I’m using a single segment envelope to modulate the amplitude of a triangle oscillator. The envelope starts at full volume, and over the duration of a note instance, fades to to silence. You can hear its affect on this except of Invention No. 1 by J.S. Bach.
Download line_envelope.csd here.
What would the same piece sound like without the envelope? To adequately demonstrate the envelope, it is necessary to listen to the same Bach excerpt using a non-enveloped triangle oscillator.
Download no_envelope.csd here.
As you can hear, that simple envelope in the first example makes a huge difference in the sound compared to the non-enveloped version. Not only does the envelope give the notes a percussive pluck-like quality, it eliminates those nasty pops and clicks you hear in the second listening example.