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acoustics
the objective study of the physical behavior of sound
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psychoacoustics
the objective study of the perception of physical sound stimuli
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equilibrium
rest position, state of rest
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elasticity
property of returning to equilibrium
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compression
pushing together
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rarefaction
stretching apart
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periodic motion
repeating cycle of vibration
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period
time required for one complete vibration
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cycle
one complete oscillation or period
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node
point of minimal vibration
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amplitude
- magnitude of displacement
- amount of vibration
- expression varies with context
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frequency
- number of cycles per unit of time
- rate of vibration
- epressed in cycles per second or Hertz (Hz.)
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wavelength
the physical length of a single cycle
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amplitude
- magnitude of vibratio (or displacement)
- it is a measurable physical property
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loudness
- subjective impression of amplitude
- this involves perception
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frequency
- rate of vibration (displacement)
- it is a measurable physical property
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pitch
- relative "highness" or "lowness" of sound
- a subjective impression of frequency
- this involves perception
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lower frequency =
- longer wavelength
- lower pitch
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higher frequency =
- shorter wavelenth
- higher pitch
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wave
transfer of energy through some medium
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physical properties of medium affects
efficiency
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velocity
- rate of travel
- 1130 ft/sec in air
- use ft/sec because it is easy to mesure delay - 1 ms per foot
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wavelength
the physical length of a single cycle
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wavelength is inversely proportional to
- frequency
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fundamental
- lowest mode of vibration involving entire body
- frequency produced by this mode of vibration
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partials
- modes of vibration involving subdivisions
- can also refer to frequencies
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overtones
frequencies produced by partial modes of vibration
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harmonics
frequencies that are whole-number multiples of the fundamental
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most sounds are
a combination of the different frequencies produced by the various modes of vibration
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just intonation
a system of musical tuning where the frequencies of notes are related by whole-number ratios
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equal temperament
a system of musical tuning where the frequencies of adjacent notes have an equal ratio
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envelope
dynamic changes in amplitude (loudness) over time
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attack
- the start of sound from state of rest to full vibration
- occurs after energy is introduced into the system
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internal dynamics
- variations and sustain
- occurs while energy is still being put into the vibrating system
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release (or decay)
return to state of rest after energy is removed from the system
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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
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Dynamic Range
the range of differences between the smallest and largest changes in something
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What dynamic rance is our hearing capable of detecting?
1 - 10,000,000
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what scale is often used to compress the dynamic range into more manageable figures?
the logarithmic scale
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the decibel
a dimensionless unit used to compare the ratio of two quantities
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the decibel is usually used in relation to what type of energy?
Acoustic energy, such as sound pressure, power, and/or intensity
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decibel notations
- dB-SPL - (acoustic) sound pressure level
- dBm - electrical power
- dBv/dBu/dBV - electrical voltage
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is the decibel a simple or accurate representation of perceived loudness?
not necessarily
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doubling sound pressure results in an
increase of 6 dB
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doubling the measurement distance results in
a decrease of 6 dB
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doubling sound power results in an
increase of 3 dB
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adding two similar (but uncorrelated) sounds at the same level generally produces an
increase of about 3 dB-SPL
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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"
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Phon (pernounced fone)
unit used to express the perceived loudness level as related to the ear's subjective impressions at various frequencies
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What is a more appropriate presentation of simple loudness than the decibel?
- Phon
- the decibel describes intensity more than loudness
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sound pressure level at 1000 Hz.
Phon level
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is the Phon a simple or accurate representation of perceived loudness?
not nexessarily
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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
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outer ear
accentuates consonants
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middle ear
impedance match to inner ear
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inner ear
frequency and intensity analysis
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brain stem
combines signals from both ears
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brain
integrates all of the signals
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premature hearing loss
hearing damage caused by exposure to loud sounds varies with loudness, frequency, duration, and exposure time
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how does prolonged exposure to dangerous noise levels affect the auditory system?
- prolonged exposure decreases auditory sensitivity
- raises the threshold of hearing (middle ear)
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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
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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
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PTS - Permanent Threshold Shift
Permanent hearing loss
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hearing loss is more pronounced in which frequency range
high frequency sensitivity
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masking
the obscuring of one sound (or aspect) by another
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pure tones close in frequency mask each other more easily than
widely-spaced tones
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pure tones mask ______ frequencies more easily than ______ frequencies
high, low
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which tones can mask broader range of frequencies?
louder tones
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which bands of noise mask like pure tones?
narrow bands
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forward masking
an initial tone can mask a subsequent tone, even if it has stopped and the two do not overlap in time
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backwards masking
a tone that begins shortly after another can mask the first
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central masking
tones heard by one ear can be masked by tones in the other
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binaural hearing (sound localization)
- hearing with the use of two ears
- inter-aural intensity differences
- inter-aural timing differences
- affected by wavelength (frequency)
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Precedence effect
directed sounds reached our ears first and indirect sounds interact with reflective objects before being heard
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how closely must sounds reach our ears to be perceived as coming from the same direction?
20 milliseconds or less
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localization becomes difficult as
the time difference increases
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