Fundamentals of Sound (pt. 3)_Amplitude Envelope

In the last two classes, we've been learning about the basic aspects of sound. So far, we have mainly been focusing on frequency and training our ears to identify specific frequencies. Today let's talk a bit about another major part of sound: amplitude! (Related to, but not to be confused with attitude.)

We already know that amplitude basically refers to loudness, right? But when you hear a sound, does it usually have the same amount of loudness throughout it? Of course, it depends on the sound - a long, steady sound like a motor running might stay at a consistent level - but usually, sounds change in amplitude throughout their duration.

For example, let's look at this waveform of an 808 snare sound:

In this picture we can clearly see how the sound quickly goes from nothing (silence) to its highest amplitude, then falls off, and then gradually trails off.

This whole process is what is called the envelope of the sound. The envelope describes the way the amplitude evolves over time. Every sound has its own unique envelope and this is partly what makes it sound the way it does. For the most part, natural sounds tend to follow this same basic pattern of

silence -> highest amplitude -> getting quieter -> trailing off

Here is another waveform of an 808 kick drum:

Now we know that a kick drum sound different from a snare, but can you see how, even though they look somewhat different, they both have that same basic shape? Here's another pic of a guitar:


ADSR
So the more specific term for describing the envelope of a sound is ADSR. This stands for Attack, Decay, Sustain, Release. Briefly:

Attack - the rise of the amplitude from the start of the sound up to the highest level.
Decay - the drop from the highest amplitude down to the average level of the sound
Sustain - the average level of the sound
Release - the fade out from the average level of the sound down to silence; on a synthesizer, this is how quickly the sound cuts off when you let go of the key

Here is a common diagram of an ADSR Envelope:
And here is what ADSR looks like on an actual waveform:

Every sound has its own natural ADSR envelope, but with digital tools like samplers and synthesizers, you can actually manipulate these parameters and modify or completely change sounds. In fact, you have been looking at and working with ADSR envelopes for months now. Can you think of where? Here's one example:
Here's another:
What do you think the Amp stands for?

So today we're going to work on a couple of projects using the ADSR envelopes on the devices in Reason to create some original sounds.