This entry explains the principles of envelopes. To begin with, an envelope signal is a subsonic, aperiodic, unipolar, and timed signal used to modify the volume curve of an audio signal. To better understand envelopes, you should also know what a gate signal is. The gate signal is a two-state signal that is capable of starting or stopping and envelope generator.
Envelopes: the Principles
An envelope generator (EG) is a device that produces envelope signals to control the output of a voltage-controlled amp (VCA). It uses its features to mimic the sounds of diverse acoustic musical instruments by controlling the volume envelope. These generators subdivide in ADSR, AHDSR, ADSDR, as well as DADSR.
The attack segment of the envelope generator starts working; people know this process as gate on. Complementary to this, the release segment of the envelope generator starts working users call it gate off. The gate signal works as a switch button. Without the gate on and the gate off functions, the envelope generator’s circuitry wouldn’t be able to start or stop.
The Terminology
As is common in the music industry, you need some terminology to facilitate the complexity of different signals and processes, such as the envelopes. Here are the definitions of four main terms:
- An ADSR is a four-segment envelope generator that controls four independent parameters of an envelope signal.
- An AHDSR includes a phase that is capable of producing punchy bass sounds. In this phase, the output remains at the maximum value between the end of the attack and the beginning of decay.
- An ADSDR includes a phase that controls the rate at which the sustain drops. As a result, one cannot reach a constant sustain. This feature is quite useful when trying to mimic the sound of musical instruments where the sound drops while the key holds. A typical example is a piano.
- A DADSR includes an initial delay between the gate on and the beginning of the attack segment.
Additionally, as you can imagine from these terms, each letter stands for something.
First, attack (A) is a time-based function that determines the time that a signal needs in order to reach its maximum value. Secondly, decay (D) is a time-based function that defines the time that a signal’s volume goes from its maximum value to a set sustain level. Thirdly, sustain (S) is a level-based function that determines the level at which a signal sustains. Fourthly, release (R) is a time-based function that defines the time that a signal needs in order to return to a zero value after the gate has been turned off.
