Introduction to sound and hearing

Question 1

Sound and vibration

Answer 1

Sound consists in propagated waves of disturbance in air pressure due to vibration (at regular intervals)

Question 2

Perceptual dimension vs Physical dimension

Answer 2

Loudness (amplitude)
Pitch
Timbre (quality of sound)
vs
intensity
frequency
spectral & amplitude envelope

Question 3

Psychophysics of sound

Answer 3

• other things being equal higher amplitude sounds will sound louder
• other things being equal higher frequency sounds will sound higher in pitch

Question 4

timbre

Answer 4

Timbre (quality) is what distinguishes two sounds of same pitch and loudness (e.g. same note played on different instruments)

Question 5

difference between periodic and aperiodic complex sounds

Answer 5

musical notes
voiced parts of speech and animal calls
vs
bangs, crashes

Question 6

Transients

Answer 6

may be periodic or aperiodic

Question 7

Waveform (time) and spectral (frequency) plots for 3 simple sounds

Answer 7

• Simple sounds
  
  • pure tones, sinusoidal waves
  • not found in nature (audiology labs and other specialist settings)

Question 8

spectrogram

Answer 8

A spectrogram is a 3D plot to show variation in both time and frequency domains

Question 9

Fourier analysis

Answer 9

• Essential technique for spectral analysis
• advanced maths
• any complex periodic sound can be made by summing together sinusoids of the appropriate frequencies and amplitudes (and phases)

Question 10

Fundamental frequency and harmonics in periodic sounds

Answer 10

• Harmonics will occur at integer multiples (fn) of the fundamental frequency (f0)
• The relative power of different harmonics will influence the timbre of the sound
• The perceived pitch will usually be f0

Question 11

Measuring sound intensity

Answer 11

• Basic unit of intensity/: watts per square metre
• Reference intensity: 10^-12 W m^-2 which is threshold for detecting 1000 Hz tone by typical listener
• sound intensity is expressed as log ratio of measured intensity to this reference
  
  • bel = log10 Im / Ir
• Log ratio is x10 to give common unit of decibel
  
  • dB = 10log10 Im / Ir

Question 12

Audibility curve

Answer 12

see pic

Question 12

Equal loudness curves

Answer 12

see pic