THEORY OF AUDIO Flashcards
WHAT IS THE FIELD OF AUDIBLE SOUND?
-between 16,000 Hz to 20,000 Hz
-20Hz to 20kHz
-mechanical energy in the form of pressure fluctuations in an elastic medium
WHAT IS ACOUSTICS?
-the wave of mechanical energy transported through a medium
WHAT IS ULTRASOUND?
- sound with frequencies higher than 20,000 Hz
- higher than 20 kHz
WHAT IS INFRASOUND?
-sound is lower than 20 Hz
WHAT ARE WAVES LIKE IN LIQUID AND GASEOUS STATES?
-progressive longitudinal waves
(particle displacement parallel to direction of wave propagation, particles oscillate back and forth between their equilibrium)
WHAT ARE WAVES LIKE IN A SOLID STATE?
-progressive transverse waves and longitudinal waves can occur
HOW ARE SOUND WAVES DISTORTIONS?
-they do not transport environment particles only their oscillating movement
WHAT ARE THE SPEEDS OF SOUND IN DIFFERENT MEDIUMS?
-slowest in gases, faster in liquids, fastest in solids
WHAT IS SOUND PRESSURE?
- sound pressure, or acoustic pressure (p),
is the local pressure deviation from the ambient (equilibrium) atmospheric pressure, caused by a sound
wave
-max speed will have a max pressure
-lowest value of air sound pressure = 2.10^-5 Pa
-The Sound Pressure Level (SPL) is a logarithmic scale of sound pressure (p) defined relative to a reference sound pressure that is approximately the sound pressure of a 1000 Hz sinusoid that is just barely audible; its unit is dB (decibel):
L = 20 log (p/p0), where p0 = 2 x 10-5 Pa
WHAT IS SOUND INTENSITY?
-the energy that passes through the unit area perpendicular to the direction of sound per unit time (W/m(squared))
-threshold of hearing = 1x10^-12 W/m^2
-proportional to the square of the amplitude of the sound wave
-as sound waves travel away from their source, the energy is spread over a greater surface area causing a reduction in the intensity of the sound wave
WHAT ARE THE DIFFERENCES BETWEEN TONE AND NOISE?
A tone is a single frequency and is regular and periodic (vocal cords), while a noise is a single tone or a collection of tones and is irregular (drums)
WHAT FREQUENCY OF SOUND IS IMPORTANT FOR SPEECH INTELLIGIBILITY AND WHICH THE EAR IS MOST SENSITIVE TO?
-2 to 4 kHz
WHAT IS THE DYNAMIC RANGE OF THE EAR?
-in the middle of the audible frequency range of about 120dB
WHAT IS FREQUENCY MASKING?
-the inability to hear two tones when they are playing simultaneously
WHAT IS THE SOUND WAVE?
-the pattern of disturbance caused by the movement of energy traveling through a medium (such as air, water or any other liquid or solid matter) as it propagates away from the source of the sound
-require a medium to transfer energy
WHAT IS PITCH OF A SOUND?
-an auditory sensation of a frequency
-depends on frequencies
-frequency is objective but pitch is subjective
-human brain determine pitch of a sound wave, it doesnt actually have one
WHAT IS TONE COLOUR / TIMBRE?
-the quality of a sound that distinguishes it from another
-determined mainly by its frequency spectrum
EG: difference between guitar and piano playing the same note
WHAT IS SOUND VOLUME?
-subjective term
-the determination of the sound which sound waves act on the pitch
WHAT IS SOUND INTENSITY?
-objective term
-sound power per unit area
-lowest value corresponds to the sound intensity threshold of hearing (0.00001 Pa), the highest sound intensity determines the threshold of pain (100 Pa)
-dynamic range of human hearing is 120dB
L= 10 log (I/I0), where I0 = 10-12 W/m2
-measured in dB HL (Thresholds below 20 dB HL are considered in the normal range, while thresholds above 20 dB HL are reported as the hearing loss (mild, moderate, severe or profound)
WHAT IS THE DOPPLER EFFECT?
-changes in the frequency of any sound or light wave produced by a moving source with respect to an observer
EG: ambulance siren being so loud when past you but quiet as it goes further away from you
COMMON DECIBEL LEVELS
WHAT IS THE WEBER-FECHNER LAW?
-perceived intensity is proportional to the logarithm of the stimulus
WHAT IS FREQUENCY?
-how often the vibration repeats
-expressed in Hz cycles per min
-distinguishes mechanical waves (infrasound, ultrasound, ultrasonic)
-at constant speed of propagation - wavelength is inversely proportional to frequency
(waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths)
-objective
WHAT FORMS THE OUTER EAR?
-pinna and auditory canal
-role is to bring the soundwave to the eardrum at the end of the auditory canal
-role of the pinna is the reflection and focusing of the incoming sound wave to the auditory canal
-tympanum is the closed end of the eardrum which enhances the sound frequency range of 2-5kHz by its resonance
-air filled
WHAT IS THE MIDDLE EAR?
-air filled cavity behind the ear drum
-3 bones: hammer, anvil, stirrup which transmit vibrations to the oval window of inner ear
-pressure amplifier due to:
(i) area amplification due to approx. 15x larger area of tympanic membrane (eardrum) in comparison to the area of oval window and
(ii) a lever-type amplification of ossicles
-eustachian tube connects the chamber of the middle ear to the back of the nasopharynx, it equalizes pressure between middle ear and surrounding atmosphere
WHAT IS THE INNER EAR?
-cochlea is set in bone and filled by fluids
-3 spaces: scala tympani, scala media and scala vestibuli
-sound is transferred by the footplate of the stapes to the oval window of the cochlea which transfers the
vibrations into one of the fluid-filled ducts of the cochlea. The fluid inside this duct is moved, flowing
against inner hair cells - which are the receptor cells of the Organ of Corti. This stimulation is then
transmitted by the auditory nerve fibres, which send the information through the auditory portion of the
eighth cranial nerve to the brain
-High frequencies are transduced at the base of
the cochlea whereas low frequencies are
transduced at the apex - due to physical characteristics of the basilar membrane
WHAT IS TONOTOPY?
-the spatial arrangement of where sounds of different frequency are processed, which begins at the cochlea
-inner ear contains vestibular apparatus (3 semi circular canals and the vestibule) - sense organ of balance, motion and gravity
-hair cells are also receptor cells involved in balance stimulated by fluid in the canals, utricle and saccule
-firing of vestibular hair cells stimulates the vestibular
portion of the eighth cranial nerve
WHAT IS CONDUCTIVE HEARING LOSS?
-transmission of sound to inner ear is impaired due to impacted cerum, ear infection, calcification of the middle ear ossicles
-loss of sensitivity across the entire range of frequencies, commonly in only one ear
DIAGNOSTIC TEST: “bone conduction test”, where sound is delivered as vibration to the skull rather than as airborne sound to the ear canal
WHAT IS SENSORY NEURAL HEARING LOSS?
-most common cause of sensory neural hearing loss is damage to sensory hair cells (predominantly outer hair cells) in the cochlea, also caused by damage to the auditory nerve.
-noise damage or age related hearing loss
-in most cases irreparable - boost sensitivity through hearing aid
WHAT IS AGE RELATED HEARING LOSS? (PRESBYACUSIS)
-ear’s outer hair cells may also simply wear out as we age, leading to age related hearing loss.
-high frequency outer hair cells tend to die off
before low-frequency ones, possibly because the high frequency outer hair cells have to work harder if their job is to amplify acoustic vibrations on a cycle by cycle basis.
-patients with age-related hearing loss often have normal sensitivity at low frequencies, but progressively poorer sensitivity for higher frequencies
WHAT IS THE WEBER HEARING TEST?
-a vibrating tuning fork is placed in the middle of the forehead and the patient is asked to report in which ear the sound is heard louder
-a normal Weber test has a patient reporting the sound heard equally in both sides, while an affected patient would report louder perception in one ear
WHAT IS A RINNE HEARING TEST?
-perception of sounds transmitted by air conduction are compared to those transmitted by bone conduction through the mastoid. Thus, one can quickly screen for the presence of conductive hearing loss.
-accompanied by a weber test to also detect sensorineural hearing loss and thus confirm the nature of hearing loss
WHAT IS PURE TONE AUDIOMETRY?
-the basic audiometric test to find out if a hearing loss is present or not
-patient wears headphones through which pure tones at different frequencies are played. Intensity is gradually reduced until hearing threshold is found.
-results expressed in decibel scale and entered into audiogram
-audiograms are routinely measured in anechoic chambers with acoustical stimulation via headphones within the frequency range of 125 Hz – 8 kHz
WHAT QUANTITY IS USED TO EXPRESS THE SUBJECTIVE PERCEPTION OF SOUND?
-loudness level
WHAT IS THE WAVELENGTH OF A SOUND WITH A FREQUENCY OF 20kHz?
-17mm
WHAT IS THE UNIT OF THE SOUND POWER LEVEL, ACOUSTIC INTENSITY LEVEL?
-dB
OBJECTIVE
WHAT IS THE UNIT OF THE OSCILLATION FREQUENCY?
-S - 1
WHAT IS THE UNIT OF SOUND INTENSITY, WAVE INTENSITY?
-W/m2
OBJECTIVE
WHAT IS THE UNIT OF PERCEIVED LOUDNESS LEVEL?
-Phon
WHAT IS THE UNIT OF FREQUENCY?
-Hz
IS THE SPEED OF ULTRASOUND THE SAME AS THE SPEED OF SOUND?
-yes
WHAT IS THE SPEED OF SOUND TRAVELLING THROUGH WATER AND AIR?
-water = 1500m/s
-air = 340m/s
-dry air = 331.5 and increases with temperature
WHAT IS THE REFERENCE FREQUENCY OF SOUND , TO WHICH SUBJECTIVELY IS COMPARED TO THE EXAMINED SOUND?
-1000Hz
ARE LEVELS OF LOUDNESS AND INTENSITY LEVEL FOR TONES WITH FREQUENCY OF 1000Hz THE SAME?
-yes
WHAT IS EQUAL LOUDNESS CONTOUR?
-curve describing the dependence of the sound intensity level on the frequency for the tones with the same level of loudness
WHAT IS THE SOUND POWER LEVEL?
- 10 X log(I/10)
WHAT DETERMINES THE VALUES OF THE LOUDNESS LEVEL?
-intensity, sound intensity and frequency
WHAT DOES ISOPHONE 50pH MEAN?
-the loudness needed at tones of different frequencies in order for us to perceive them as being equally as loud as a tone with the frequency of 1000Hz and the sound intensity of 50dB
WHAT IS THE INTENSITY OF NORMAL CONVERSION?
-50dB
WHAT ARE THE SUBJECTIVE UNITS?
-phon and sone
WHAT ARE OBJECTIVE UNITS?
-dB and w/m2
HOW DO WE PERCEIVE SOUND THAT ARE THE SAME INTENSITY BUT DIFFERENT FREQUENCIES?
-different loudness
WHAT IS SOUND?
-a mechanical wave of frequencies within the human audible range - need a medium in which energy can travel through
WHAT IS THE RELATIONSHIP OF THE SPEED OF SOUND WITH TEMPERATURE?
-they both increase together in a linear way
WHAT KIND OF SCALE IS THE SOUND PRESSURE LEVEL?
-logarithm
IS LOUDNESS SUBJECTIVE OR OBJECTIVE AND WHAT IS IT RELATED TO?
-subjective and is related to sound pressure level, sound duration and frequency
-stated in phons
WHAT ARE TONIC RECEPTORS?
-adapt slowly to prolonged stimulation
EG: pain reeptors
WHAT ARE PHASIC RECPTORS?
adapt rapidly to prolonged stimulation
EG: Pacinian corpuscles which sense vibration and pressure
WHAT DOES THE SPEED OF SOUND INCREASE WITH?
increasing temperature
-> lowest in gases
WHAT IS ACOUSTIC IMPEDANCE?
ratio of sound pressure to particle velocity
-the product of the density of the medium and the speed of sound
-the resistance the sound waves meet from the medium they are passing through
-determines absorption of sound and acoustic transmission and reflection
WHAT IS THE ABSORPTION OF SOUND?
property of a material that changes the acoustic energy of propagating sound waves into another form of energy
WHAT IS WAVELENGTH?
distance between consecutive points of the same phase
-determined by frequency and speed of sound
-wavelength inversely proportional to frequency
λ = v/f
WHAT IS ACOUSTIC PRESSURE?
local pressure deviation from equilibrium atmospheric pressure
-caused by a sound wave
-measured with microphone
WHAT IS LOUDNESS?
perception of amplitude in decibel (Db) or Phons
WHAT IS HEARING LOSS USUALLY RELATED TO?
hair cells in ear
-outer hair cells extremely fragile or damage to auditory nerve
-sensory neural hearing loss usually cannot be cured but conductive hearing loss can be
-noise damage indicated by 4kHz
WHAT IS TYMPANOMETRY?
objective test of middle ear function, eardrum / tympanic membrane in particular, and the conducting bones by creating variations of air pressure in the ear canal
-measure of energy transmission
-diagnosis of otitis media by demonstrating the presence of middle ear effusion
WHAT ARE AUDITORY PROVOKED POTENTIALS?
trace the signal generated by a sound through the ascending auditory pathway
-generated in cochlea and ends in cortex
WHAT IS THE UNIT FOR ACOUSTIC POWER?
Watt W
WHAT IS THE UNIT FOR VOLUME?
Son
WHAT IS THE UNIT FOR VOLUME LEVEL?
Phon Ph
WHAT WAVES DOES THE AUDITORY SYSTEM CONSIST OF?
mechanical waves
WHAT FREQUENCIES ARE HUMASN MOST SENSITIVE TO?
200 to 5000 Hz
WHAT IS THE AUDITORY THRESHOLD FOR SOUND PRESSURE?
0.00002 Pa
WHAT IS AMPLITUDE?
how much energy is contained in the displacement of molecules that make up sound waves
L = 10 log(I/I0) in dB
I0 = 10^-12 W/M2
-highest amplitude is about 120 dB = threshold of pain
WHAT DOES THE PRE PRINTED CURVE OF AN AUDIOGRAM MEAN?
normal threshold of hearing
WHAT CAN WEBER FECHNERS LAW BE ASSOCIARUED WITH?
audiometry
WHAT DOES VELOCITY OF SOUND DEPEND ON?
its medium
