PerLecture 10 - Sound and Hearing Lecture Notes

Vocabulary flashcards covering the physics of sound, human ear anatomy, hearing theories, and sound localization cues based on the lecture transcript.

Sound (Sensation)

An auditory event or sensation evoked by the oscillation of pressure, stress, particle displacement, or particle velocity propagated in a medium with internal forces.

Sound Waves

Oscillation of air pressure within the audible frequency range that causes waves of compression while leaving air molecules in roughly the same place.

Newton ($N$)

A unit of force defined as $1\,\text{kg} \times 1\,\text{m/s}^2$.

Pascal ($Pa$)

A unit of pressure defined as $1\,\text{N/m}^2$.

Micropascal ($\mu\text{Pa}$)

A unit of pressure used in acoustics where $1\,\mu\text{Pa} = 10^{-6} \times \text{N/m}^2$.

Hearing Threshold (Pressure)

$20\,\mu\text{Pa}$ at a frequency of $1-2\,\text{kHz}$.

Pain Threshold

$10^8\,\mu\text{Pa}$ or $10\,\text{Pa}$.

Speed of Sound

$1238\,\text{km/h}$.

Decibel ($\text{dB}$)

A logarithmic unit for sound pressure that provides a more linear representation compared to micropascals.

Hearing Threshold (Decibels)

$0\,\text{dB SPL}$.

Decibel SPL Formula

$$\text{dB SPL} = 20 \times \log_{10}(\frac{P}{P_0})$$

Doubling sound level

Results in an increase of approximately $6\,\text{dB}$.

Pure Tone

A sound consisting of a single harmonic (sine) wave.

Complex Tone

A combination of sine waves and non-harmonic periodic waves.

Noise

Sound characterized by non-periodic vibrations.

Amplitude

The magnitude of a sound wave, which corresponds to perceived loudness.

Timbre

The quality of a sound (e.g., voice or instrument) consisting of a combination of all frequencies, found only in complex tones.

Fundamental Frequency

The lowest frequency of a periodic waveform.

Overtones

Frequencies that are higher than the fundamental frequency.

Harmonic Overtones

Integral multiples of the fundamental frequency.

Octaves

A doubling of the frequency; two tones one octave apart are considered similar in pitch.

Shepard Tone

An auditory illusion of infinitely increasing pitch created by increasing octaves fading in at low frequencies and out at high frequencies.

Outer Ear

Responsible for protecting the eardrum, amplifying useful frequencies, and sound localization.

Middle Ear

Contains auditory ossicles (bones) that transmit vibrations to the oval window, amplifying sound pressure by $20-50\times$.

Cochlea

Acts as a frequency analyzer where pressure from the oval window causes the basilar membrane to wobble and bend cilia hair.

Bekesy’s Place Theory

Theory stating the base of the basilar membrane vibrates to high frequencies and the apex (far end) vibrates most to low frequencies.

Phase Locking

A signaling method where fibers in the auditory nerve fire specifically at the peak of basilar vibration.

Presbycusis

Hearing loss caused by hair cell damage from noise exposure over time.

Binaural Cues

Sound localization cues based on the difference in sounds reaching the two ears.

Monaural Cues

Sound localization cues based on the pattern of sound from one ear.

Inter-aural time difference (ITD)

The difference in time it takes for sound to reach each ear; best for low frequencies and horizontal localization.

Inter-aural level difference (ILD)

The difference in loudness between ears caused by the head hindering sound waves; best for high frequencies and horizontal localization.

Inter-aural phase shift

A localization cue that is most effective for low pitch sounds.

Zones of confusion

Occurs when a listener cannot distinguish if a sound is in front or behind them because the listener and sound source are approaching each other.

Head-Related Transfer Functions (HRTF)

A monaural cue where the outer ear helps judge sound elevation based on how sound waves bounce.