Volume shaping - ADSR

Volume Shaping in Synthesizers

Once we've worked with tone generation via our oscillator and tone shaping via our filter, we want to look at volume shaping.

Understanding Volume Shaping

Volume shaping is done via the amplifier module of a synthesizer and is responsible for controlling the level or loudness of a signal over time.

Comparing Sound Characteristics

Let's take, for instance, the sound of a violin:

• A violin sound will slowly ramp up to a peak (or maximum level) as the bow is dragged across the string.
• It is sustained for a period of time until the bow is moved away from the string, at which point it cuts off quite abruptly.

In contrast, hitting a snare drum with a drumstick results in:

• A very fast peak level with no sustain.
• The sound immediately dies out.

These two sounds clearly have different characteristics over time. Synthesizers can emulate these sonic characteristics by providing control over different parts: the beginning, the middle, and the end of a sound, specifically, the level of that sound over time.

The Envelope Generator

This is achieved by using a component called an envelope generator. The envelope of a sound can be thought of as its loudness or its contour, and how that is shaped over time.

This brings us to the concept of ADSR:

• Attack
• Decay
• Sustain
• Release

These are the envelope controls that you will usually find on a synthesizer.

Attack

• Definition: Sets the time it takes for the signal to rise from an amplitude of 0 to 100% (full amplitude).
• Examples: It's going to be shorter for a percussive sound, but longer for a rising pad or string-type sound.

Decay

• Definition: Sets the time it takes for the signal to fall from 100% amplitude to the next stage, which is the sustain level.

Sustain

• Definition: Sets the steady amplitude level produced when a key is held down.
  • This is not a length of time as such but a volume level at which the sound sustains after the decay phase.
  • In most sounds, it's going to be lower than the attack volume, but it could be the same or even higher if desired.
  • The sustain phase can theoretically last forever if you were to continually hold a key down.

Release

• Definition: Sets the time it takes for a sound to decay when the key has been released.

Caveats

It's important to bear in mind that some sounds don't actually have all four phases. For instance:

• A wood block only has an attack and a decay phase.
• An organ has an attack phase, a sustain phase, and a release phase, but it has no decay phase.

So, you're not always going to get all stages, and it depends on what type of sound you're trying to create.

Conclusion

Using just these three building blocks of subtractive synthesis, tone generation, tone shaping, and volume shaping (or an oscillator, a filter, and an envelope generator), it's possible for us to create a huge range of sounds, both natural and artificial.