1.1 Music and Sound

Question 1

How is sound formed?

Answer 1

Through vibrations that require a medium to travel through.

Question 2

What wave type does sound travel as and what happens?

Answer 2

Longitudinal, otherwise known as compression waves. In which a series of compressions (regions of higher pressure than the surroundings) and rarefactions (regions of lower pressure than normal).

Question 3

What is a wavelength?

Answer 3

The distance between two successive compressions is one wavelength and the symbol is λ.

Question 4

What is the frequency?

Answer 4

The number of vibrations per second or the number of compressions passing a fixed point per second and is measured in herts (Hz).

Question 5

What equation links frequency and wavelength to wave speed?

Answer 5

c = f x λ.

Wave speed = frequency x wavelength.

Question 6

What is infrasound?

Answer 6

Sound below 20 Hz is below human capabilities of hearing and known as infrasound.

Question 7

What is ultrasound?

Answer 7

Sound above 20 kHz is above human capabilities of hearing and known as ultrasound.

Question 8

When sounds are turned into an electrical signal, with a detector such as a microphone, how can the frequency be measured?

Answer 8

Using an oscilloscope. From the time-base setting the period (the time for one vibration, T) can be measured and hence the frequency (f) can be found using the equation. Period = 1/frequency

Question 9

What is the time-base of an oscilloscope?

Answer 9

This is a circuit which controls how long it takes for the trace to cross the screen horizontally.

Question 10

How is the pitch of sound from a musical instrument produced?

Answer 10

From the fundamental frequency plus harmonics.

Question 11

What is a harmonic?

Answer 11

Multiples of the fundamental frequency.

Question 12

What are sound waves of certain pitches that make a pleasant sound together known as?

Answer 12

Consonant or harmonics.

Question 13

What do consonants/harmonic sound waves form the pass of?

Answer 13

Musical interval.

Question 14

What is a musical interval?

Answer 14

An interval between two notes on a musical scale determined by the ratio of the frequencies of the notes.

Question 15

What is quality sometimes called?

Answer 15

Timbre- it is an important factor that gives a musical instrument or voice its unique character.

Question 16

What three aspects is the timbre of a sound made up of?

Answer 16

The harmonics present, the attack and decay of the sound and the vibrato.

Question 17

How can harmonics be analysed?

Answer 17

Using Fourier analysis- this characterises the wave in terms of the different amplitudes of the frequencies that make up the harmonics of the sound wave.

Question 18

How can harmonics be synthesised electronically?

Answer 18

Fourier synthesis- this is a process by which any regular sound can be reproduced by adding regular alternating voltages together.

Question 19

What is the attack of sound?

Answer 19

A measure of how quickly it reaches its peak amplitude or loudness.

Question 20

What is the decay of sound?

Answer 20

A measure of how long it takes to die away.

Question 21

What is vibrato?

Answer 21

A periodic change in the pitch of the waveform as the sound continues to be produced.

Question 22

What is a tremolo?

Answer 22

A name to describe a periodic change in amplitude- musicians will often do this deliberately to give expression or variation to music.

Question 23

Middle C has a frequency of 256 Hz. What are the frequencies of the Cs which are one and two octaves higher than middle C?

Answer 23

512 Hz and 1024 Hz.

Question 24

Define octave.

Answer 24

Musical interval between harmonics that have frequency f and 2f. Doubling/ halving of frequency.

Question 25

Define period.

Answer 25

Time for one complete cycle.

Question 26

State what is meant by the threshold of hearing.

Answer 26

Minimum intensity which can be detected by normal human ear.

Question 27

A sound source emits a continuous tone at a constant frequency.
An observer, walking at a constant speed from the source to a wall, hears a regular rise and fall in the intensity of the sound.
Explain how the minima of intensity occur.

Answer 27

Standing waves formed as a result of superposition.
Two waves, opposite directions.
They are permanently out of phase and destructively interfere.