Vibration, Sound, and Hearing

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Vibration, Sound, and Hearing
2012-12-13 15:33:20

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  1. acoustics
    the objective study of the physical behavior of sound
  2. psychoacoustics
    the objective study of the perception of physical sound stimuli
  3. equilibrium
    rest position, state of rest
  4. elasticity
    property of returning to equilibrium
  5. compression
    pushing together
  6. rarefaction
    stretching apart
  7. periodic motion
    repeating cycle of vibration
  8. period
    time required for one complete vibration
  9. cycle
    one complete oscillation or period
  10. node
    point of minimal vibration
  11. amplitude
    • magnitude of displacement
    • amount of vibration
    • expression varies with context
  12. frequency
    • number of cycles per unit of time
    • rate of vibration
    • epressed in cycles per second or Hertz (Hz.)
  13. wavelength
    the physical length of a single cycle
  14. amplitude
    • magnitude of vibratio (or displacement)
    • it is a measurable physical property
  15. loudness
    • subjective impression of amplitude
    • this involves perception
  16. frequency
    • rate of vibration (displacement)
    • it is a measurable physical property
  17. pitch
    • relative "highness" or "lowness" of sound
    • a subjective impression of frequency
    • this involves perception
  18. lower frequency =
    • longer wavelength
    • lower pitch
  19. higher frequency =
    • shorter wavelenth
    • higher pitch
  20. wave
    transfer of energy through some medium
  21. physical properties of medium affects
  22. velocity
    • rate of travel
    • 1130 ft/sec in air
    • use ft/sec because it is easy to mesure delay - 1 ms per foot
  23. wavelength
    the physical length of a single cycle
  24. wavelength is inversely proportional to
    • frequency
  25. fundamental
    • lowest mode of vibration involving entire body
    • frequency produced by this mode of vibration
  26. partials
    • modes of vibration involving subdivisions
    • can also refer to frequencies
  27. overtones
    frequencies produced by partial modes of vibration
  28. harmonics
    frequencies that are whole-number multiples of the fundamental
  29. most sounds are
    a combination of the different frequencies produced by the various modes of vibration
  30. just intonation
    a system of musical tuning where the frequencies of notes are related by whole-number ratios
  31. equal temperament
    a system of musical tuning where the frequencies of adjacent notes have an equal ratio
  32. envelope
    dynamic changes in amplitude (loudness) over time
  33. attack
    • the start of sound from state of rest to full vibration
    • occurs after energy is introduced into the system
  34. internal dynamics
    • variations and sustain
    • occurs while energy is still being put into the vibrating system
  35. release (or decay)
    return to state of rest after energy is removed from the system
  36. comb filtering
    • a destructive interferece that results when a sound is added to a phase-shifted (usually time-delayed) version of itself
    • results in a series of notch filters that "comb" out a series of frequencies, thus changing the tonal (spectral) nature of the sound
    • can be caused by direct sound combining with reflected sound (as reflected sound travel a longer distance, they are delayed)
    • can be caused by the introduction of time-delay in audio processing, such as the intentional use of effect processors or the inherent latency (delay) introduced by digital audio systems
  37. Dynamic Range
    the range of differences between the smallest and largest changes in something
  38. What dynamic rance is our hearing capable of detecting?
    1 - 10,000,000
  39. what scale is often used to compress the dynamic range into more manageable figures?
    the logarithmic scale
  40. the decibel
    a dimensionless unit used to compare the ratio of two quantities
  41. the decibel is usually used in relation to what type of energy?
    Acoustic energy, such as sound pressure, power, and/or intensity
  42. decibel notations
    • dB-SPL - (acoustic) sound pressure level
    • dBm - electrical power
    • dBv/dBu/dBV - electrical voltage
  43. is the decibel a simple or accurate representation of perceived loudness?
    not necessarily
  44. doubling sound pressure results in an
    increase of 6 dB
  45. doubling the measurement distance results in
    a decrease of 6 dB
  46. doubling sound power results in an
    increase of 3 dB
  47. adding two similar (but uncorrelated) sounds at the same level generally produces an
    increase of about 3 dB-SPL
  48. Equal Loudness Principle
    • Auditory sensitivity varies with frequency
    • Our hearing mechanism is less sensitive to low and high frequencies then mid-range frequencies
    • These sensitivity differences lessen as loudness increases
    • One reason why people think loud music "sounds better"
  49. Phon (pernounced fone)
    unit used to express the perceived loudness level as related to the ear's subjective impressions at various frequencies
  50. What is a more appropriate presentation of simple loudness than the decibel?
    • Phon
    • the decibel describes intensity more than loudness
  51. sound pressure level at 1000 Hz.
    Phon level
  52. is the Phon a simple or accurate representation of perceived loudness?
    not nexessarily
  53. Equal Loudness Contours
  54. Sone
    • perceived loudness
    • unit used to express comparative loudness of multiple sounds
    • arbitrary scale created to provide a linear representation of perceived loudness
    • 1 sone = 40 phons
    • every 10 phons (10x intensity) = 2x sones
  55. The Auditory System
  56. outer ear
    accentuates consonants
  57. middle ear
    impedance match to inner ear
  58. inner ear
    frequency and intensity analysis
  59. brain stem
    combines signals from both ears
  60. brain
    integrates all of the signals
  61. premature hearing loss
    hearing damage caused by exposure to loud sounds varies with loudness, frequency, duration, and exposure time
  62. how does prolonged exposure to dangerous noise levels affect the auditory system?
    • prolonged exposure decreases auditory sensitivity
    • raises the threshold of hearing (middle ear)
  63. TTS - Temporary Threshold Shift (aka auditory fatigue)
    • creates a false perception of actual loudness
    • necessitates compensation (turning the volume up even more)
    • could last minutes, hours, or days
  64. Tinnitus
    • ringing, whistling, or buzzing in the ears after prolonged exposure to loud sounds
    • could last minutes, hours, or days
    • indicates damage is either imminent or has already occured
  65. PTS - Permanent Threshold Shift
    Permanent hearing loss
  66. hearing loss is more pronounced in which frequency range
    high frequency sensitivity
  67. masking
    the obscuring of one sound (or aspect) by another
  68. pure tones close in frequency mask each other more easily than
    widely-spaced tones
  69. pure tones mask ______ frequencies more easily than ______ frequencies
    high, low
  70. which tones can mask broader range of frequencies?
    louder tones
  71. which bands of noise mask like pure tones?
    narrow bands
  72. forward masking
    an initial tone can mask a subsequent tone, even if it has stopped and the two do not overlap in time
  73. backwards masking
    a tone that begins shortly after another can mask the first
  74. central masking
    tones heard by one ear can be masked by tones in the other
  75. binaural hearing (sound localization)
    • hearing with the use of two ears
    • inter-aural intensity differences
    • inter-aural timing differences
    • affected by wavelength (frequency)
  76. Precedence effect
    directed sounds reached our ears first and indirect sounds interact with reflective objects before being heard
  77. how closely must sounds reach our ears to be perceived as coming from the same direction?
    20 milliseconds or less
  78. localization becomes difficult as
    the time difference increases