L1 Sound

Question 1

Sound is produced by a rapid variation in the average _______ or ________ of air molecules above and below the current ____________.. Minute changes in __________ are referred to as sound pressure and the fluctuations in pressure as sound waves

Answer 1

Sound is produced by a rapid variation in the average density or pressure of air molecules above and below the current atmospheric pressure.. Minute changes in atmospheric pressure are referred to as sound pressure and the fluctuations in pressure as sound waves

Question 2

Higher pressure areas = ________
Lower pressure areas = ________

Answer 2

Higher pressure areas = ‘compressions’
Lower pressure areas = ‘rarefractions’

Question 3

What sort of tone is a sine wave?

Answer 3

A pure tone

Question 4

What 3 parameters uniquely define a sine wave, and are used to describe complex sounds?

Answer 4

Period
Amplitude
Phase

Question 5

What is the period of a sound

Answer 5

The period is the duration of one cycle of a sine wave
It is the time it takes for an air molecule to oscillate back and forth one time.

Question 6

What is amplitude?

Answer 6

The strength or level of sound pressure.
Amplitude—distance between the resting position and the maximum displacement of the wave.

Question 7

What is phase?

Answer 7

Phase – Phase specifies the location or timing of a point within a wave cycle of a repetitive waveform.

Question 8

What is frequency?

Answer 8

The number of complete cycles in a second
Unit of measurement: 1 Hz = 1 period per second
- Frequency is inversely related to the period (T) i.e frequency = 1/period (F=1/T)

Question 9

What is a waveform? What are the disadvantages of using a waveform?

Answer 9

Way of displaying a sine wave. Display of time against amplitude
Difficult to get frequency from this

Question 10

What is a spectrum?

Answer 10

Way of displaying a sine wave.
Focuses on what is happening in terms of freq (freq domain). Display of freq against amplitude within each freq component represented by a vertical line – easier to work out frequencies of sounds

Question 11

What are complex sounds?

Answer 11

Sounds made up of many sine waves
‘Any perodic vibration, no matter how complicated in seems, can be built up from sinusoids whose frequencies are integer multiples of a fundamental frequency, by choosing the proper amplitudes and phases’

Question 12

What is a complex periodic waveform?

Answer 12

• made up of sine waves w freqs that are multiples of each other e.g 100Hz, 200Hz, 500Hz)
• Component sine waves = ‘harmonics’ and the components are said to be ‘Harmonically related’

Question 13

What is the fundamental frequency?

Answer 13

Freq of repetition of the waveform. All other harmonics are multiples of this freq.
Fundamental freq is always the first harmonic

Question 14

Different types of complex periodic waveforms (e.g sine, square, sawtooth) have different _______

Answer 14

Timbres

Question 15

What are complex aperiodic waveforms?

Answer 15

• made up of sine waves w freqs not related to each other e.g 100Hz, 222, 278 etc
• The complex sound sounds discordant; the waveform does not repeat in a regular pattern
• Aperiodic sounds which contain many components that are not harmonically related are perceived as ‘noise’ (e.g pink noise, white noise)

Question 16

Why is dB a ‘relative measure’?

Answer 16

a decibel value is always relative to a reference level so it describes a ratio between 2 sounds

Question 17

What is a logarithmic scale used for in sound?

Answer 17

A logarithmic scale is used to compare ratios in a decibel scale. This compresses an enormous range of ratios into something manageable

Question 18

What are the 2 essential components for resonance to occur?

Answer 18

Sound sources & resonating cavity

Question 19

What is a Helmholtz resonator?

Answer 19

It is a resonator which responds best to (ie amplifies the intensity of) a frequency determined by the size of the resonator: ‘resonant’ frequency

Question 20

What is the ‘response’ of a resonator?

Answer 20

the effect of the resonator on the intensity of the input sound (e.g a response of 2 means it will be twice as intense as before it went through the resonator)

Question 21

How many resonant frequencies does a simple resonator have?

Answer 21

1

Question 22

How many resonant frequencies does a complex resonator have?

Answer 22

more than one resonant frequency

Question 23

How many peaks will the transfer function of a simple resonator have?

Answer 23

1

Question 24

How many peaks will the transfer function of a complex resonator have?

Answer 24

Multiple peaks

Question 25

What happens when we put a signal through a complex resonator?

Answer 25

The harmonics close in frequency to the resonant frequency of the resonator are amplified (become more intense) while those far from the resonant frequency are reduced in intensity. This is a ‘linear system’ can change amplitude but not frequency of the sounds

Question 26

In the source-filter model of speech, what is the source and filter?

Answer 26

Source - Sound made in larynx (for voiced sound) OR in the oral tract (for voiceless sounds)
Filter - Vocal tract

Question 27

What type of waveform does speech produce?

Answer 27

Sawtooth (complex periodic wave)

Question 28

Women and children’s vocal folds are shorter and typically vibrate faster than men’s. How does this change the spectrum?

Answer 28

Question 29

Resonant peaks are called:

Answer 29

Formants

Question 30

What type of waveform do voiceless consonants produce?

Answer 30

Complex aperiodic waveform

Question 31

Question 32

What is pitch?

Answer 32

quality of sound governed by rate of vibrations producing it; the degree of highness or lowness of a tone. In voiced speech mostly related to the perception of voiced source characteristics

Question 33

What is timbre?

Answer 33

the character or quality of a musical sound or voice as distinct from its pitch and intensity

Question 34

What is a resonant peak?

Answer 34

A peak, or boost, in frequency response created by a filter.