The Volume Envelope
The amplifier is the latest stage in the process and is often labelled, VCA, DCA, AMP, EG, ENV / ENVELOPE or ADSR. The amplifier section controls the volume of the sound, but it is more than just a straight volume control. The Amplifier uses an ‘Envelope Generator' to control the overall loudness (or amplitude) of the sound over time.
To understand how an envelope works, we need to go back to how we perceive the volume of sound. For example the sound of a piano has a strong emphasis at the start of the sound but then doesn't sustain for very long, whereas the sound of a car engine passing by will gradually sound louder and louder as the car approaches and then slowly disappear in volume.
A Volume envelope in a synth is designed to help us shape the volume of the sound from the moment you press a key until you release it.
Envelope generators
Envelope generators
are used to help the synthesiser produce expressive sounds. A most basic synth has at least one envelope generator that controls the volume of the sound, but envelope generators do not only control the volume, in some devices, they can also control other parameters.
It is quite common to find two envelope generators in many devices, one to control the volume and the other to control the filter cut off for example. Today we will look at how to use the envelope to shape the volume of a sound.
Envelope generators
are triggered by the keyboard; when you press a key, it sends a ‘trigger' message to the envelope generator; it begins the generator's process of creating an envelope. As long as the key on the keyboard is held down, another message is sent to the envelope generators. The message tells the generators that the note is still being played and the envelope being generated will stay open until this message ceases. When the message stops (you release the key), the envelope will go into its final stage.
ADSR
Nowadays, there are many variations of envelopes available. However, the most common envelope generator has four parameters: Attack time, Decay time, Sustain level, and Release time, usually called ADSR envelope.
The diagram below shows how an ADSR envelope is used to control the volume of the sound, from when you hit a key until you release it.
ADSR: The four phases of an ADSR envelope. Notice how they relate to a key being pressed.
Attack: This is the length of time required for the sound to reach its initial maximum volume. Obviously it will be very short for a percussive sound.
Decay: This is what happens immediately after a sound hits its maximum volume level in the attack phase. It's the time taken for the volume to reach a second volume level known as the sustain level.
Sustain: This is not a length of time but a volume level at which the sound sustains after the decay phase. In most sounds is it lower than the attack volume, but it could be the same or even higher. Usually, it's the volume at which a sound plays while a key is being held down. This phase can, theoretically, last forever, or at least until you get tired of holding down the key.
Release: This is the final phase, again measured in time, and is the time it takes the volume to reach zero after you release the key.
Saving Presets
Don't forget to save any sounds which you create. Obviously you may have spent a lot of time creating a great bass or synth sound, and ultimately you want now to be able to reload it when you need it. This is part of building your own sound library.
First, click on the settings drop down menu and select Save Settings As; We saw that some basic knowledge about subtractive synthesis can go a long way in creating the sounds that we hear from our favourite producers and the sounds that we hear in our own minds. The use of a simple envelope (ADSR) to control volume allows the manipulation of amplitude over time, adding expression to sounds created with oscillators and filters. This is known as modulation.