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.

Fundamentals of Sound (pt. 1)_Frequency & Amplitude

So far we've discussed a bunch of different topics, from music theory to hip hop history to navigating software. Today we're going to talk a little about the science of sound.

What is sound?

On the most basic level, sound is the vibration of molecules. Since we live in an air-filled atmosphere, sound for us is usually the vibration of air molecules.

Whenever there is any kind of impact or friction in our air-filled environment, the air molecules get compressed and are pushed out of their normal positions. They then react by springing back in the other direction. Same concept as a pulling a piece of string tight and then plucking it; the molecules swing back and forth.
When molecules vibrate, they get pushed out of their normal positions and bump into their neighbor molecules. This causes the neighbor molecules to vibrate, and bump into their neighbors, which bump into their neighbors, and so on. These vibrations spread out in all directions in waves, sort of like dropping a rock in a pool of water. This is how the sound gets to your ears. The waves move outward from the sound source at a steady rate, but they get weaker and weaker (quieter and quieter) as they move farther and farther away...

If we try to draw a picture of a sound vibration, we get something like this:
A picture like this is called a waveform. By now, we're all used to seeing waveforms from our recordings in Pro Tools. And as you probably remember from editing, when you zoom in really close, then we see something like this:



What this picture is showing you is one vibration, or cycle. If we think back to the example of the plucked string, this is the equivalent of the string being plucked, then swinging out in the opposite direction, then coming back to its original position. But when you pluck a string, does it just vibrate once and then stop? Of course not! It vibrates many times, but let's keep this idea of cycles in mind as we get to the main topic for today...

FREQUENCY and AMPLITUDE

Here are the basics of what you need to understand:

Frequency = pitch (Hz)

Amplitude = loudness (dB)

Frequency is the number of cycles that happen in one second. The higher the pitch of the sound, the more cycles (aka vibrations) are happening in each second. Therefore, a note played on a high pitched instrument, like a flute, is going to have many more of these cycles in one second than a low pitched instrument, like an 808 bass drum. In the waveform diagram below, the horizontal (left to right) axis is showing frequency. You can see certain sections where the cycles are pressed more tightly together than in other parts. Do you think these parts are lower or higher in pitch compared to the parts where the cycles are spaced out more?The unit of measurement of cycles per second is Hertz (Hz).

Amplitude is the amount of energy that goes into making the sound, i.e. how LOUD the sound is. If I slam my hand down on the table, it makes a much louder sound than if I lightly tapped the table with my finger. This is because I put a lot more energy into making the sound and our ears interpret the amount of energy as loudness. In the waveform diagram, the height of the wave is showing you the amplitude.The unit of measurement of amplitude is the decibel (dB).

Last and thing to know for today:

The human range of hearing is approximately 20Hz to 20,000Hz.

With this information, we can start to get into really working with sound and making it do what we want! (Mwah ha ha!).

Next time, we will get into the wonderful world of harmonics...