The Physics of Music

Music is the art of sound, so let's start by talking about sound

Sound is invisible waves moving through the air around us.

When something vibrates, it disturbs the air molecules around it. The disturbance moves through the air in waves

These sound waves hit your eardrum

How the ear works-

Transverse Waves

Most kinds of waves are transverse waves. In a transverse wave, as the wave is moving in one direction, it is creating a disturbance in a different direction.

Longitudinal waves

But sound waves are not transverse. Sound waves are longitudinal waves. If sound waves are moving south, the disturbance that they are creating is making the air molecules vibrate north-and-south

Diagramming waves

It is very difficult to show longitudinal waves clearly in a diagram, so most diagrams, even diagrams of sound waves, show transverse waves. It's particularly hard to show amplitude in longitudinal waves, so we will use both types of diagrams as we go along.

Categories of sound

Surf rolling down a beach, leaves rustling in the wind, a book thudding on a desk, or a plate crashing on the floor all make sounds, that is, create sound waves--

But, these sounds are not music

Music is sound that's organized by people on purpose. Therefore, the sound waves for music are more organized--

A tone is a specific kind of sound

The vibrations that cause it are very regular - all the same size and same distance apart.

White Noise

The sound of surf, rustling leaves, or bubbles in a fish tank are also white noise, the term that scientists and engineers use for continuous sounds that are mixtures of all the different wavelengths

Categories

So the two broad categories of sound are

Noise Tones

So Star Wars is a lie?

Since sound waves need a medium, that is something to push around, like air, there can be no sound in a vacuum--

Sound waves as Tones

Another way to picture a sound wave is

Notice that the movement is regular—same speed, same height.

When sound waves make a tone-

They have certain characteristics.

The distance between the tops of two waves (the crests) is the same and can be measured. This is known as the wavelength.

The height of the waves is also consistent and can also be measured. This measurement is called the amplitude.

High and low tones

The frequency of the wavelengths determines the pitch (degree of highness or lowness) of the tone.

Sound file of tones covering entire range of human hearing.

Turn that down!!!

The amplitude effects the volume of a tone—the higher the amplitude, the louder.

Amplifier…Amplitude…get it?

How musicians talk about Amplitude

Dynamics is the musical term for the amplitude (volume level) of music.

Amplitude vs Dynamics The amplitude of a sound is a particular

number, usually measured in decibels, but dynamics are relative; an orchestra playing fortissimo is going to be much louder than a single violin playing fortissimo. The exact interpretation of each dynamic marking depends on: comparison with other dynamics in the music the typical dynamic range for that instrument or

ensemble the abilities of the performer(s)

Thought experiment

Try imagining yourself as one of the particles that a wave is disturbing (a water drop on the surface of the ocean, or an air molecule). As it comes from behind you, a transverse waves lifts you up and then drops you down; a longitudinal wave coming from behind pushes you forward and then pulls you back.

In other words--

A pebble dropped into water creates a transverse wave.

A Tsunami creates a longitudinal wave

Waves and musical instruments When the wave hits something, it can

bounce (reflection) or be bent (refraction). In fact, you can "trap" waves by making them bounce back and forth between two or more surfaces. Musical instruments take advantage of this; every musical instrument is in some way a trap for sound waves.

Timbre

One of the basic elements of music is called color, or timbre (pronounced TAM-ber).

Color includes all the aspects of a sound that do not have anything to do with how high or low it is, how loud or soft, or how long or short.

Timbre

In other words, if a flute plays a note, and then an oboe plays the same note, for the same length of time, at the same loudness, you can still easily tell the two notes apart, because a flute sounds different from an oboe. This difference is the timbre of the sound.