Transcript physics of music

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.