chapter 11 pt 1 Flashcards
physical definition of sound
pressure changes in the air or other medium
perceptual definition
the experience we have when we hear
how do loud speakers produce sound
by cycling through the processes of condensation and rarefication to increase and decrease hair pressure in a pattern
the pattern of air pressure changes is called a sound wave
remember: air pressure changes but the air molecules dont change place, they just move back and forth
condensation
first part of a loud speaker making sound - the diaphragm of the speaker moves out, pushing air molecules together - increase in density = local increase in air pressure above atmospheric pressure
rarefaction
second part of a loud speaker making sound
- the diaphragm moves in, pulling the air apart - air molecules spread out to fill in the increased space - decreased density = decrease in air pressure
amplitude
difference in pressure between high and low peaks of a wave
perception of amplitude
loudness
pure tone
a simple sound that occurs when changes in air pressure occur in a since wave pattern
fundamental building blocks of sound - but rare in the environment
what is the measure of loudness
decibel dB - the decibel scale relates the amplitude of the stimulus with the psychological experience of loudness
frequency
number of cycles within a given time period
oscilliations/second
how is frequency measured
in Hertz (Hz) - 1 Hz is one cycle per second
is perception of pitch related to frequency or loudness
frequency
tone height
the increase in pitch that happens when frequency is increased
fundamental frequency
the repetition rate and is called the first harmonic
periodic complex tones
consist of several pure tones called harmonics
additional harmonics
multiples of the fundamental frequency
additive synthesis
process of adding harmonics to create complex sounds
frequency spectrum
display of harmonics of a complex sound
missing fundamental
can still hear a tone without the fundamental frequency
because even when wave form changes, periodicity remains the same
what is the perceptual quality most closely related to the level or amplitude of an auditory stimulus
loudness
human hearing range
20 to 20 000 Hz
audibility curve
different frequencies take different amounts of sound in order for us to be able to hear them. The audibility curve shows the threshold of hearing in relation to frequency
changes on this curve show that humans are most sensitive to 2000 to 4000 Hz
periodic waveform
a pattern of repeating pressure changes
the repetition rate of a periodic waveform is the fundamental frequency
first harmonic
pure tone with a frequency equal to the fundamental frequency, also called the fundamental of the tone
the fundamental of a complex tone has a frequency which matches the repetition rate of the complex tone
higher harmonics
pure tones with frequencies that are whole number multiples of the fundamental frequency
adding higher harmonics to the fundamental results in the waveform of a complex tone
frequency spectra
a plot that indicates the amplitudes of the various harmonics that make up a complex tone - each harmonic is indicated by a line that is positioned along the frequency axis , with the height of the line indicating the amplitude of the harmonic
why do tones remain the same, even when we remove the first harmonic/fundamental?
because removing a harmonic changes a tone’s waveform, but the rate of repetition remains the same
remember the spacing between harmonics equals the repetition rate - and removing the fundamental doesn’t change the spacing
what are the perceptual aspects of sound
loudness: differences in the perceived magnitude of a sound
pitch: involves differences in the low to high quality of sounds
auditory response area
the portion of the audibility curve that contains tones we can hear
tones below the audibility response area are too low to hear and tones above are too painful/damage our auditory system
threshold of feeling
the upper boundary of the auditory response curve that contains high amplitude tones that are painful/can cause damage to the auditory system
equal loudness curves
a part of the audibility curve that indicates the sound levels that create the same perception of loudness at different frequencies
determined by presenting a pure tone of one frequency and having ps adjust the level of pure tones with frequencies across the range to match its loudness
pitch
property of auditory sensation in terms of which sounds may be ordered on a musical scale extending from low to high
its variation is associated with musical melodies
tone chroma
the perceptual similarity of notes separated by one or more octaves (tones that have frequencies that are binary multiples of each other)- notes with the same letter (A,B,C D, E, F, G)
notes with the same chroma have fundamental frequencies that are separated by a multiple of two
timbre
the quality that distinguishes between two tones that sound different even though they have the same loudness, pitch and duration
differences in timbre are illustrated by the sounds made by different musical instruments
attack and decay of a tone
attack: buildup of sound at the beginning of a tone
decay: decrease in sound at the end of a tone
periodic sounds
a sound stimulus in which the pattern of pressure changes repeats
aperiodic sounds
sound waves that do not repeat
no perception of pitch
- door slamming shut, bunch of people talking at the same times, static on a radio
outer ear
pinnae - ‘ear’ part - structures that stick out of the head
auditory canal - tube that protects the tympanic membrane/eardrum and keeps everything at a constant temperature
also enhances the intensities of some sounds by means of resonance
sound first enters here
resonance
occurs in the auditory canal when sound waves that are reflected back from the closed end of the auditory canal interact with sound waves that are entering the canal
the interaction reinforces some of the sound’s frequencies, with the frequency that is reinforced the most being determined by the length of the canal
resonant frequency
the frequency that is most strongly enhanced by resonance
the resonance frequency of a closed tube is determined by the length of the tube
middle ear
small cavity that separates the outer and inner ears
contains the ossicles:
malleus - set into vibration by the tympanic membrane
incus - receives vibrations from the malleus
stapes - receives vibrations from the incus and transmits its vibrations to the inner ear by pushing on the membrane covering the oval window
why are the ossicles necessary
they concentrate the vibration of the large tympanic membrane onto the much smaller stapes, increasing the pressure - important because the inner ear is filled with fluid, so it takes more pressure to vibrate it
they also create a lever action - ex. pushing on the long end of the board makes it possible to lift a heavy weight on the short end
- basically amplifying a small force - the lever action of the ossicles amplifies the sound vibrations reaching the tympanic inner ear
middle ear muscles
the smallest skeletal muscles in the body found in the middle ear
attached to the ossicles, and at very high sound levels they contract to dampen the ossicle’s vibration
- reduces the transmission of low frequency sounds and helps to prevent intense low frequency components from interfering with our perception of high frequencies
inner ear
innermost division of the ear containing the cochlea and receptors for hearing
cochlea
snaillike structure in the inner ear that contains the basilar membrane and the organ of corti
its upper half and lower half is separated by the cochlear partition, which extends almost the entire length of the cochlea, from the base near the stapes to its apex at the far end
organ of corti
the major structure of the cochlear partition, containing the basilar membrane, the tectorial membrane, and the receptors for hearing
basilar membrane
a membrane that stretches the length of the cochlea and controls the vibration of the cochlear paritition
tectorial membrane
a membrane that stretches the length of the cochlea and is located directly over hair cells - vibrations of the cochlear partition cause the tectorial membrane the bend the hair cells by rubbing against them
tectorial membrane
a membrane that stretches the length of the cochlea and is located directly over hair cells - vibrations of the cochlear partition cause the tectorial membrane the bend the hair cells by rubbing against them
stereocilia
small processes at the tips of hair cells which bend in response to pressure changes
the stereocilia in the the tallest row of outer hair cells are embedded in the tectorial membrane, and the stereocilia in the rest of the outer hair cells and all of the inner hair cells are not
what does the motion of the basilar membrane do and how is it started
it sets the organ of corti into an up and down vibration and it causes the tectorial membrane to move back and forth
the movement causes the stereocilia that are connected to the tectorial membrane to bend (and the other stereocilia)
it is set into motion by vibrations that cause the oval window to move, transmitting those vibrations to the liquid inside the cochlea
transduction in the ear
bending of the stereocilia one way causes tip inks to stretch, which opens tiny ion channels in the membrane of the stereocilia
when the stereocilia bend the other way, the links slacken, the ion channels close and ion flow stops
the back and forth bending causes alternating bursts of electrical signals
the electrical signal result in the release of neurotransmitters at the synapse separating the inner hair cells from the auditory nerve fibers, causing the fibers to fire
potassium ions flow into the cell and an electrical signal results
what is the pattern of auditory nerve firing
fibers fire in synchrony with the pressure changes of a pure tone
stereocilia bend one way to pressure increases and fall back the other way in response to pressure decreases
this is called phase locking because firing occurs in the place as the sound stimulus
