ADSR Envelope and Gate Signals

This article will discuss the basics of both envelopes and gate signals. Both concepts are closely related, and combining them 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 considered 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 the signal takes to reach the internally determined maximum value.  

• Decay (D): Decay is a time-based function. It determines when 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 sign 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 gate and EG are closely related 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.  

Common Usage and Types

The most common use of an envelope generator is to control the output of a voltage-controlled amplifier (VCA). Furthermore, different parameters, like attack, release, etc., mimic the sounds of various acoustic instruments by controlling the volume envelope.   Here are a few other types of EG’s apart from ADSR:  

• AHDSR: The extra ‘H’ is basically a phase where the output remains at the maximum between the end of the attack and the beginning of decay. This can be especially used to create punchy bass sounds.

• ADSDR: 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 the piano, where the sound dies out while the key is held longer.  
• DADSR: The extra ‘D’ stands for delay. So, this is an initial delay between the gate and the start of the attack segment.