This article will discuss the basics of both envelopes and gate signals. Both the concepts are closely related and putting them together will be more meaningful.
What is an envelope signal?
An envelope signal is a subsonic, aperiodic, unipolar positive and timed signal. Therefore, it can be thought of as a fluctuating DC signal that can be used to alter the volume curve of an audio signal.
ADSR Envelope Generator (EG)
An envelope generator is a device that generates an envelope signal. It is usually abbreviated as ‘EG’
An ADSR is a four-segment envelope generator. This means that it provides control over four independent parameters of the envelope signal.
- Attack (A)
Attack is a time-based function. It determines the time taken by the signal to reach the internally determined maximum value.
- Decay (D)
Decay is a time-based function. It determines the time in which the volume goes from max to the programmed sustain level.
- Sustain (S)
It is a level-based function. It determines the level at which the signal sustains.
- Release (R)
It is a time-based function. It determines the time that the signal takes to get to zero value once the gate has been turned off.
Now let us look at what a signal means.
Gate Signal and its relation to EG
It is a two state signal that is used to stop or start an envelope generator. ‘Gate on’ means that the attack segment of the EG starts working. ‘Gate off’ means the release segment of the EG starts working.
The reason why the gate and EG are closely related is because without the gate on or off, the EG circuitry will never start or stop. It basically acts as a switch to make EG work.
The Following picture explains all the segments of an ADSR and how the gate signal helps to make it work:
Common usage and types
The most common use of an envelope generator is to control the output of a voltage controlled amplifier (VCA). Furthermore, the different parameters like attack, release etc. are used mimic the sounds of various acoustic instruments by controlling the volume envelope.
Here are a few other types of EG’s apart from ADSR:
The extra ‘H’ is basically a phase where the output remains at the maximum between the end of attack and beginning if decay. This can be especially used to create punchy bass sounds.
The extra ‘D’ basically controls the rate at which the sustain dies down hence it does not have a constant sustain. This is especially useful to mimic the sound of instruments like piano where the sound dies out while key is held for longer.
The extra ‘D’ stands for delay. So this has an initial delay between the gate on and start of the attack segment.
Additional Resources & Source Texts
Sound syntheses and sampling – Martin Russ