Chapter 10: Sound And The Ears Flashcards
Sources of Sound
In order:
- Sound is initiated by movement that disturbs air molecules
- Molecules collide with other air molecules resulting in air pressure that propagates outward from source
- As the sound wave travels outward form the source in all directions, the wave front resembles a sphere that grows continuously larger
- Sound energy at any given point on the wave from decreases with distance from the source (inverse square law)
Sound Waves
Waves of pressure changes in air caused by vibrations of a source
Cycle
In sound wave, a repeating segment of air pressure changes
Inverse square law
Energy of sound decreases in proportion to square of distance from source
3 physical dimensions of sound:
- Frequency- pitch
- Amplitude- loudness
- Waveform- timbre
Periodic Sound Waves
Waves in which the cycles of compression and rarefaction repeat in regular (periodic) fashion
Pure Tone
Sound wave in which air pressure changes over time according to sine wave (sinusoid)
Frequency
Physical dimension of sound that is related to perceptual dimension of pitch
- expressed in hertz (number of cycles/ second of periodic sound wave)
Pitch
Perceptual dimension of sound that corresponds to physical dimension of frequency
- perceived highness/ lowness of sound
Hertz (Hz)
- physical unit used to measure frequency
- cycles per second
Amplitude
Difference between maximum and minimum sound pressure in sound wave
- physical dimension of sound that is related to perceptual dimension of loudness
Loudness
Perceptual dimension of sound that corresponds to physical dimension of amplitude
Decibels (dB)
- physical unit used to measure sound amplitude
- logarithmically related to sound pressure measured in micropascal
Waveform
Physical property for perceptual correlate for timbre
Periodic sound waves
Waves in which the cycles of compression and rarefaction repeat in a regular, or periodic, fashion
Compression
Region in a longitudinal wave where the particles are closest together
Rarefaction
Region in a longitudinal wave where the particles are furthest apart
- follows period of compression
Frequency and pitch
- the frequency of a pure tone is the physical dimension related to the perceptual dimension of pitch and expressed in hertz (Hz)
- Young human adult sound detection range: 20- 20000 Hz
- The loudest sounds a human can hear are approximately 1 million times the amplitude of the softest sounds that can be heard
Amplitude and Loudness
- Amplitude: expressed as dB SPL= 20 log (p/po)
- Loudness: perceptual dimension of sound that is related to physical dimension of amplitude
- how intense or quiet a sound seems
Audibility Curve
- shows minimum amplitude at which sounds can be detected at each frequency
- horizontal axis of this graph uses a logarithmic scale to allow the clear presentation of a wide range of frequencies
Equal Loudness Contours
Curve showing amplitude of tones at different frequencies that sound about equally loud
Phon
Unit of loudness
- loudness of tones is numerically equal to amplitude of 1000 Hz tones that sound equally loud
Fourier
Provided that waveforms of most periodic sounds have a more complex shape than a sine wave
- Fourier analysis
- Fourier spectrum
- Fundamental frequency
Fourier Analysis
Mathematical procedures for decomposing a complex waveform into collection of sine waves with various frequencies and amplitudes
Fourier Spectrum
Depiction of amplitudes at all frequencies that make complex waveform
Fundamental frequency
Frequency of lowest- frequency component of complex waveform
- determines perceived pitch of sound
Harmonic
Component frequency of complex waveform that is an integer multiple of the fundamental frequency
- First harmonic- fundamental frequency
- what we’re most likely to hear - Second harmonic- fundamental frequency x2
Timbre
Difference in sound quality between two sounds with same pitch and loudness
- for complex periodic sounds, timbre is mainly due to differences in relative amplitudes of sounds’ overtones - perceptual dimension of waveform
- illusion of the missing fundamental
- manner of onset and offset
Illusion of the missing fundamental
Shows that the auditory system uses patterns of frequencies in a sound’s harmonics as part of pitch perception
Manner of onset and offset
Manner of onset (attack) and offset (decay) also affect timbre perception
Complex waveforms
- do not sound like pure tone
- have sound quality that depends on frequency and amplitude of their fundamental frequency and each overtone
Sounds that differ in timbre
Two complex sounds that have the same pitch and loudness but do not sound the same due to differences in relative amplitudes of various overtones
Anatomy of the ear
Outer ear
Middle ear
Inner ear
Outer ear
Pinna, auditory canal, outer tympanic membrane
Middle ear
Air-filled chamber with ossicles
Inner ear
Cochlea and semicircular canals
Acoustic Reflex
Allows us to not amplify noise in times of really loud noises using ossicles
Pinna
Outermost portion of the ear; shape can modify incoming sound and contribute to sound localization