Sound Production

Question 1

What is sound?

Answer 1

A local pressure disturbance in a continuous medium (air/sea) that contains frequencies in the range of 20 to 20,000 Hz (the audible range)

Question 2

Who does the definition of sound apply too?

Answer 2

Only humans, not all humans can hear sounds of that range

Question 3

What is the audible range for sound?

Answer 3

20-20,000hZ

Question 4

What is a single sound wave caused by?

Answer 4

An increase in pressure at a certain point in an elastic medium which causes a domino effect

Question 5

What happens if a perturbation is repeated periodically?

Answer 5

It generates a series of sound waves - vibrating source, causes an increase in pressure

Question 6

What does a wave tell you?

Answer 6

The crests respond to high pressure points and the troughs correspond to low pressure points

Question 7

Where does sound propagate from?

Answer 7

The source at equal speed in all three dimensions

Question 8

What are sound waves?

Answer 8

Spherical waves - because sound expands in lots of different ways, not just in a straight line

Question 9

What does the speed at which sounds propagates depend on?

Answer 9

The type, temperature and pressure of the medium through which it propagates

Question 10

What is the speed of sound in dry air (20 degrees)

Answer 10

343m/s - 1 meter every 2.9 milliseconds - this is so fast that speed is almost irrelevant

Question 11

What is the simplest representation of sound? - how we record sound

Answer 11

A waveform - the temporal variation of sound pressure as a fixed point in space

Question 12

What happens when we record sound?

Answer 12

We record a temporal variation - sound pressure at a fixed point in space

Question 13

What are most sounds generated by?

Answer 13

Produced by oscillators - means that you give a little energy now and then and they will work at their own frequency (being on a swing)

Question 14

What are most sounds?

Answer 14

Periodic - one that repeats itself at regular intervals

Question 15

Why are oscillators useful?

Answer 15

Because you don’t need to control them, just give a little energy and the will move back and forth, creating a periodic sound wave

Question 16

The pressure variation of a periodic sound is an oscillation with a given..

Answer 16

Period

Amplitude

Question 17

The period of a sound wave

Answer 17

The duration of a oscillation cycle

Can be measured as the time between two peaks

Question 18

The frequency of sound

Answer 18

Used more than period
The number of air pressure oscillation cycles per second - it is the opposite of the period
Frequency = 1 divided by period by T

Question 19

What is one single oscillatory cycle per second?

Answer 19

1hz - not audible

Question 20

Types of oscillatory cycles

Answer 20

125 (the fundamental frequency is male voice) = 125hZ
200 - fundamental frequency in female, 200Hz
2000 - some bird calls, 2000 hz
15000 - some bat calls - 15000

Question 21

What does fundamental frequency mean?

Answer 21

The lowest frequency which is produced by the oscillation of an object

Question 22

The amplitude of sound

Answer 22

This is the loundess
This is the magnitude of the change in sound pressure within the wave - maximum amount of pressure at any point in the sound wave
Also called sound pressure level

Question 23

How is amplitude measured?

Answer 23

Decibels

Question 24

What is loudness?

Answer 24

The perceptual correlate of amplitude - it isn’t a scientific measure, it is subjective, non linear perceptual attribute which varies with period, frequency and distance

Question 25

What are the ways of representing sound?

Answer 25

Waveforms
Spectrograms
Spectrums

Question 26

What is a waveform?

Answer 26

Represents sound in terms of time and amplitude (energy)

Question 27

What is a spectrogram?

Answer 27

Represents energy (amplitude) as a function of time and frequency
Energy is represented by different shades of grey, if dry what, no energy at time or frequency. Energy isn't present at all frequencies

Question 28

What is a spectrum?

Answer 28

Measures energy as a function of frequency - time is removed

A peak tells us how much energy there is at each Hz

Question 29

What are simple sound waves?

Answer 29

Pure tones
Simple frequency tones with no harmonic content - sine wave
Only has energy at one frequency e.g. a beep
Nothing above or below 1.5 kZ - frequency of a single tone
don’t use this for communicating

Question 30

What are complex sounds?

Answer 30

Animals humans and most musical instruments usually generate sounds which have energy at more than one frequency - complex sounds
Composed of more than one tone
They are periodic and repeat themselves
have harmonics and a fundamental frequency