Envelope

All sounds have a shape, and this shape is really important for what we hear.

The Life of a Sound

Every sound has a beginning, a middle and an end. All sounds change over time. Changes over the life of a sound are described by the envelope.

Different sounds have different envelopes. The shape of the envelope affects the sound that we hear.

Composition Tip

The shape of a sound’s envelope will affect how it sounds.

When composing, try to use a range of sounds that have different envelopes. This will give your compositions a range of different sound types, and help you to create interesting contrasts (see also: Timbre).

To read more about Sound Types, please click here.

Breaking Down the Envelope

To help us talk about sound envelopes, we can break them down into four clear sections:

  • Attack – The speed with which a sound begins.
  • Decay – The time it takes for the attack to drop to a steady state.
  • Sustain – A steady period in the life of a sound.
  • Release – The gradual decay into silence.

Every sound will naturally have these sections, but in different proportions.

Attack & Sustain

The two most important aspects of the envelope are the Attack and Sustain. Let’s look at these in more detail:

Attack

Sometimes the attack might be very short, other times it might be long. The attack is one of the most important parts used by the brain when it tries to recognise sounds.

Fast Attack

This sound has a fast attack. Listen to how it very quickly begins. It has a very sharp and crisp sound.

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Slow Attack

This sound has a slow attack. You can hear how it slowly emerges. It has a very soft and smooth sound.

Sounds with a fast attack are crisp, while those with a slow attack appear more smooth and rounded.

Sustain

Sounds that ring out have a long sustain.

Long Sustain

This sound has a long sustain. Listen to the steady tone.

But if we reduce the sustain, we focus attention on the attack.

Short (or No) Sustain

The sound does not ring out, but begins to fade away almost immediately.

Sounds with a long sustain will ring out for a long time. Sounds with a short sustain will be very short and quick.

Listening Example

If we listen to the sound of a bell, we can hear its long resonant sustain.

Original Bell

This bell sound has a long sustain, continuing to ring out for a long time as its vibrations slowly dies out.

But, if we dampen that same bell by pressing a cloth against it, we remove all of that sustain and keep mainly the attack.

Dampened Bell

This time, the cloth prevents the bell from vibrating and ringing out. It dampens the sustain and almost stops it completely.

By dampening the vibrations with a cloth, we have changed the envelope of the bell sound and highlighted the attack of the sound.

Decay and Release

The other two parts of the envelope – Decay and Release – also play a part in how a sound appears to us, but they are more subtle.

Finally the sound fades out. We often pay a lot of attention to how sounds begin and ignore the way in which they end.

However, the duration of release can make a difference to the sound that we hear.

A sound with a long release will last for a long time and gradually fade out. While sounds with a short release will fade quickly.

Transformation of an Envelope

Because the envelope is a really important property of sound, changes and transformations which affect a sound’s envelope have a big impact on the final sound that we hear.

Reverse

When we reverse a sound, we flip the envelope. So the attack becomes the release and what was the release becomes the attack.

Original Sound

Listen to the envelope of this original sound. There is a fast attack, followed by a slow decay – sustain – release.

Reversed Envelope

This sound has been flipped in reverse, so the envelope is now backwards. In contrast to the original sound, we now have a slow attack, followed by a quick decay – release. (There isn’t even really any sustain at all).

Reversed sounds are used quite a lot in different styles of music. The flipping of the envelope makes a big difference and can create some really fantastical new sounds.

Splice

Splicing a sound can allow us to remove or rearrange individual parts of the sound’s envelope. By removing portions of the envelope, we can dramatically transform how we hear a sound.

Original Sound

This sound has a clear and strong attack sound. You can hear the ‘thwack’ as the glass is hit.

Because the attack is one of the most important pieces of information used by the brain in recognising where a sound comes from, by removing the attack, we can hide the source of the sound.

Attack Removed by Splicing

This sound has had the attack portion spliced off. We no longer hear the loud ‘thwack’ of the glass being hit, only the ringing sustain of the glass.

Removing (or transforming) the attack portion of a sound’s envelope can help us to hide the original source of the sound, and can focus the listener’s attention on different aspects of the sound.

Extra

The shape of a sound envelope is directly related to how an object vibrates and makes sound. The properties of the object and the way in which it is encouraged to make sound will all affect the properties of the final envelope.

For example: Think of the difference in sound between plucking a string (to get a sharp, pizzicato sound) and bowing a string (to get a smooth, steady sound).

All sounds have a shape, and this shape is really important for what we hear.

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