Week 4: Hearing
The Ear and Hearing - Three base concepts of hearing include the Primitive Level, Symbolic Level and the Warning Level. By the Primitive Level we mean a situation where whatever noise you hear has little meaning to you and can be comforting or even irritating depending on your reaction to the noise. But none the less you know you can hear it. By Symbolic Level we mean a situation where two different noises have came together to convey the same thing. The example in this case is the spoken word of a car radio telling you traffic is bad and the actual sound of the traffic as you approach, both of which tell you that heavy traffic is ahead. By Warning Level we mean a situation where a certain sound has caused you to follow a certain instruction just by hearing it. For example hearing a siren approaching from behind and pulling over to let the vehicle pass.
How Does Normal Hearing Work - There are three main parts of the anatomy of an ear. You have the outer ear, the middle ear and of course the inner ear (cochlea). The outer ear is made of three parts; the pinna, ear canal and the eardrum. The middle ear is made of two parts; the ossicles and the ear drum and finally the inner ear is made up of the cochlea, the auditory nerve and the brain.
So, sound waves enter the ear canal and cause the ear drum to vibrate. This causes the ossicles in the middle ear to move. The end of the ossicles hits the membrane window of the cochlea and cause the fluid inside to move. This fluid movement causes a response in the hearing nerve,
The Journey of Sound Waves - You ear actively funnels sound waves into your outer ear canal. These waves then travel down this passage until they eventually hit the ear drum and cause it vibrate. As the ear drum vibrates your ossicles starts to move. Following this the vibrations are passed to a thin layer of tissue at the inner ear known as the oval window. As soon as the oval window reacts tot he vibrations wave-like motions are started in the fluid in your cochlea.
Your Body's Microphone - The main organ of hearing is the spiral organ known as the Corti that runs through your cochlea. The Corti is made up of thousands of tiny sensory hair cells attached to a membrane. A tiny sensory hair emerges from each cell and drill through a second membrane above. When the fluids in the cochlea are moving the first membrane in the Corti vibrates and squashes the sensory hairs against the second membrane. The movement of these hairs is then transformed into nerve impulses that travel through nerves into the brain.
Locating Sounds - Due to having two ears we are able to actually locate the sound of a sound. For example, if a sound is originating from the right then it will obviously reach your right ear before your left and as such will be louder in this ear. Through this we can tell the sound came from the left.
Source: http://www.electric-avenues.com/hearing.html
Source: http://www.hearinglink.org/how-the-ear-works
A Complete Structure of the Ear -
Source: http://2eyeswatching.com/2012/11/16/this-insect-has-human-ears/
Cochlea and Frequencies -
Source: http://www.ifd.mavt.ethz.ch/research/group_lk/projects/cochlear_mechanics
Cochlear Structures -
Source: https://www.studyblue.com/notes/note/n/cmscds-3213-study-guide-2012-13-marks/deck/9718820
Schematic of Auditory Periphery -
The Impedance Matching Mechanism of the Middle Ear. Impedance matching is a very important function of the middle ear. The middle ear transfers any incoming vibrations from the tympanic membrane to the oval window. The tympanic membrane is low impedance and the oval window is high impedance. The middle ear makes an efficient impedance transformer. This means that it will convert low pressure vibrations into high pressure vibrations that are suitable for moving the cochlear fluids. The impedance of the cochlear fluids is equal to sea water. Due to this only 0.1% of energy would be transmitted.
The two processes that are involved in the impedance matching are.
1. The area of the tympanic membrane is larger than that of the stapes foot plate in the cochlea. The forces that get collected in the ear drum are placed directly over a smaller area and due to this the pressure in the oval window increases.
2. The second process is the lever action of the middle ear bones. The incus is much shorter than the malleus and as such this produces a lever action that increases both the force and decreases the velocity at the stapes. With the malleus being 2.1 times longer than the incus then the force is multiplies by 2.1.
The ear functions as a type of fourier analysis device with the mechanism of the inner ear converting any of the mechanical waves into electrical impulses used to describe the intensity of sound in terms of frequency. Ohm's law of hearing is that the perception of the tone of a sound is a function of the amplitudes of the harmonics and not of the phase relationships between them. This is consistent with the place theory of hearing. This correlates the observed pitch to the position along the basilar membrane of the inner ear that is stimulated by the corresponding frequency.
Features of Auditory Processing -
A two channel set of time-domain signals in contiguous, non-linearly spaced frequency bands. Seperation of: left from right ear signals, low from high frequency information and timing from intensity information. Re-integration and re-distribution at various specialized processing centre in the hierarchy. - Directly from the lecture.
Audible Frequency Range -
Source: http://www.howequipmentworks.com/physics/medical_imaging/ultrasound_imaging/ultrasound.html
"Normal" Hearing in Humans -
Hearing Threshold - 0 dB SPL = 20?Pa at 1 kHz.
Dynamic Range - 140 dB(Up to Pain Level)
Frequency Range - (In Air) ~ 20 Hz to 20 kHz
Most Sensitive Frequency Range - ~ 2 kHz to 4 kHz
Frequency Discrimination - ~ 0.3% at 1 kHz
Minimum Audible Range - ~ 1 degree
Minimum Binaural Time Difference - ~ 11?s
Human Hearing and Speech Data -
Source: http://upload.wikimedia.org/wikipedia/commons/b/bc/Audible.JPG
Source: http://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/HearingLoss.svg/500px-HearingLoss.svg.png
Human Hearing and Speech -
Human hearing covers a wide range of frequencies. About 20 Hz to 20 kHz. In this range there are frequencies generated by conversational speech. The lowest sound pressure level humans can hear is the hearing threshold. Normally 1 kHz to 4 Khz.
MPEG/MP3 Audio Coding -
Source: http://folk.uio.no/alexanje/research/formats/
The two processes that are involved in the impedance matching are.
1. The area of the tympanic membrane is larger than that of the stapes foot plate in the cochlea. The forces that get collected in the ear drum are placed directly over a smaller area and due to this the pressure in the oval window increases.
2. The second process is the lever action of the middle ear bones. The incus is much shorter than the malleus and as such this produces a lever action that increases both the force and decreases the velocity at the stapes. With the malleus being 2.1 times longer than the incus then the force is multiplies by 2.1.
The ear functions as a type of fourier analysis device with the mechanism of the inner ear converting any of the mechanical waves into electrical impulses used to describe the intensity of sound in terms of frequency. Ohm's law of hearing is that the perception of the tone of a sound is a function of the amplitudes of the harmonics and not of the phase relationships between them. This is consistent with the place theory of hearing. This correlates the observed pitch to the position along the basilar membrane of the inner ear that is stimulated by the corresponding frequency.
Features of Auditory Processing -
A two channel set of time-domain signals in contiguous, non-linearly spaced frequency bands. Seperation of: left from right ear signals, low from high frequency information and timing from intensity information. Re-integration and re-distribution at various specialized processing centre in the hierarchy. - Directly from the lecture.
Audible Frequency Range -
Source: http://www.howequipmentworks.com/physics/medical_imaging/ultrasound_imaging/ultrasound.html
"Normal" Hearing in Humans -
Hearing Threshold - 0 dB SPL = 20?Pa at 1 kHz.
Dynamic Range - 140 dB(Up to Pain Level)
Frequency Range - (In Air) ~ 20 Hz to 20 kHz
Most Sensitive Frequency Range - ~ 2 kHz to 4 kHz
Frequency Discrimination - ~ 0.3% at 1 kHz
Minimum Audible Range - ~ 1 degree
Minimum Binaural Time Difference - ~ 11?s
Human Hearing and Speech Data -
Source: http://upload.wikimedia.org/wikipedia/commons/b/bc/Audible.JPG
Source: http://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/HearingLoss.svg/500px-HearingLoss.svg.png
Human Hearing and Speech -
Human hearing covers a wide range of frequencies. About 20 Hz to 20 kHz. In this range there are frequencies generated by conversational speech. The lowest sound pressure level humans can hear is the hearing threshold. Normally 1 kHz to 4 Khz.
MPEG/MP3 Audio Coding -
Source: http://folk.uio.no/alexanje/research/formats/
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