Analog ear
Encyclopedia
An analog ear or analog cochlea is a model of the ear
or of the cochlea
(in the inner ear
) based on an electrical, electronic or mechanical analog
. An analog ear is commonly described as an interconnection of electrical element
s such as resistor
s, capacitor
s, and inductor
s; sometimes transformer
s and active amplifier
s are included.
collects sounds like a horn and guides them to the eardrum
. Vibrations of the drum are conveyed to the inner ear
via a system of bones called ossicles
. These leverage the larger motions of the eardrum
to the smaller vibrations of the oval window
. This window connects to the cochlea
which is a long dual channel arrangement consisting of two channels separated by the basilar membrane
. The structure, about 36 mm in length, is coiled to conserve space. The oval window
introduces sounds to the upper channel. The lower channel has a round window
but this is not driven by the bones of the middle ear. The far end of the structure has a hole between the two channels called the helicotrema
that equalizes slowly varying pressures in the two channels. A series of sensory hair cells along the basilar membrane
respond to send neural pulses towards the brain.
. He used glass slides, razor blades, and an elastic membrane to represent the helicotrema
. He could measure vibrations along the basilar membrane
in response to different excitations frequencies. He found that the pattern of displacements for given frequency sine wave along the basilar membrane
rose somewhat gradually to a peak and thereafter fell. High frequencies favored shorter distances from the oval window
than did lower ones. Frequency values approximate a logarithmic distribution with distance.
Detailed discussions of the direct models by von Bekesy will be found in his book, "Experiments in Hearing", McGraw-Hill, 1960. Also see his article and others in S. S. Stevens, "Handbook of Experimental Psychology", John Wiley and Sons, 1951. This handbook is singled out as a major source of information on speech and hearing, word recognition, and other topics as well as data on the human ear.
A direct (mechanical) model uses the variables of air and water pressure, fluid velocity and viscosity, and displacement. An electrical analog model uses a different set of variables, namely, voltage and current. The outer and middle parts of the ear can be represented with a collection of coils, capacitors, and an ideal transformer to represent the leveraging effect of the ossicles
. This circuit terminates with a capacitor representing the oval window
. From there, the two channels are represented with a sequence of inductors and resistors for fluid flow within each channel with the two channels joined with a sequence of series resonant RLC circuits. Voltages across capacitances represent basilar membrane
displacements. Element values along the cochlea are tapered in a logarithmic fashion to represent lowering frequency responses with distance.
The pattern of voltages along the basilar membrane
can be viewed on an oscilloscope. Average values can be obtained with rectification and shown as patterns using a high speed commutator. The analog ear shows patterns that closely follow those observed by Georg von Békésy
on his more direct model.
The first relatively complete model was constructed in the early 1960s at the University of Arizona by two graduate students and their faculty mentor with support from the newly established Air Force Bionics
program. This work was first summarized in a report: "An Electronic Analog of the Ear", Technical Documentary Report No. AMRL
-TDR
-63-60, June, 1963, Biophysics Laboratory, 6570-th Aerospace Medical Research Laboratories, Aerospace Medical Division, Air Force Systems Command, by E. Glaesser, W. F. Caldwell, and J. L. Stewart. The report contains an extensive list of references. The work was also reported at Bionics
symposia.
, perhaps caused by non-symmetric motions of sensory cells resulting in non-symmetric motions of the basilar membrane
. Difference frequencies could be generated as are observed in the human. Some difference frequencies originating in the cochela can be observed in the outer ear
.
Neural signals responding to motions of the basilar membrane
show responses in one direction as in rectification. At all but low frequencies, the neural measure averages over multiple cycles to give the equivalent of rectification followed by averaging (low-pass filtering). Over the entire cochlea
, response shows as a pattern that varies more slowly that the applied frequency but that does follow the envelope of the applied signal. Each group of cells can give rise to a semi-periodic wave that can be analyzed by neurons in the brain. The total pattern that arises from a sound can thus be thought of as a two-dimensional pattern in time with one axis being the distance along the basilar membrane
and the other being distance along some sequence of neurons. These patterns, varying at rates less than lower audio frequencies, have shapes that can be identified much like patterns in vision. The concept of the "neural analyzer" as an extension of cochlear patterns is discussed in U. S. patent 3,387,093, "Speech Bandwidth Compression System", June 4, 1968. (Filed in 1964.)
It was found that the analog ear with its asymmetric overlapping bands was more reliable in identifying speech sounds that is a conventional frequency spectrum
. The second formant is the most significant single measure. Speech sounds of interest include whispered
and clipped speech. See "Speech Processing with A Cochlear-Neural Analog, John L. Stewart, 1967, Technical Documentary Report No. AMRL
-TR
-66-229. An article published in the journal Behavioral Science studied constraints to sensory discrimination imposed by two kinds of neural noise. Considerable information on speech patterns and recognition is reported by a number of different authors in the "Handbook of Experimental Psychology" referred to above.
Applications were made to animals and insects with appropriate ear models. See "Aural Systems Simulation for Birds and Insects," Robert L. Lucas, John L. Stewart, and Richard A. Schaeffer. Technical Report AFAL-TR-66-12. January, 1966. Another study using the analog ear was "Simulating Mechanisms in Animal Echoranging," John L. Stewart and James M. Kasson. Technical Report AMRL
-TR
-68-194. September, 1969.
Many reports, articles, and patents followed the research as cited in the reports listed here. The last full report employed a relatively early version of a computer program written in time-shared BASIC
. See "A Theory and Physical Model for Cochlear Mechanics," John L. Stewart. Acta Oto-Laryngologica, Supplement 294, 1972. Parameters of the analog ear and patterns obtained with the computer program are shown. Patterns and parameters given in this report are sufficient to reproduce analog ears.
Stewart also self-published several books, doing business as Santa Rita Technology, and later as Covox, including The Analog Ear Story and The Analog Ear–brain System in 1964, and The Bionic Ear in 1979.http://books.google.com/books?q=inauthor%3Ajohn+inauthor%3Astewart+intitle%3Aear
The research resulting from analog ear studies fueled the creation of special sounds for use in repelling birds and other pests. Sounds were synthesized to follow natural bird calls but were of a switching kind. The concept is similar to the use of a babble of human voices for jamming another person's communications. The "Av-Alarm" was the principal product. It was also adapted to the transonic and ultrasonic regions with a device called "Transonic."
The research also led to development of an early speech word recognizer that operated with 8-bit computers as well as later ones based on 16 bit processors. The product line was developed by Covox, Inc. with product names of "Speech Thing" and "Voice Master."
A number of U.S. (and foreign) patents on topics related to Stewart's analog ear were granted. In the order of filing dates starting in 1962, numbers are 3,294,909, 3,325,597, 3,387,093, 3,432,618, 3,378,700, 3,483,325, 3,459,034, 3,543,138, and 3,510,588.
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
or of the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
(in the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
) based on an electrical, electronic or mechanical analog
Analogue electronics
Analogue electronics are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two different levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal...
. An analog ear is commonly described as an interconnection of electrical element
Electrical element
Electrical elements are conceptual abstractions representing idealized electrical components, such as resistors, capacitors, and inductors, used in the analysis of electrical networks...
s such as resistor
Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
s, capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s, and inductor
Inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
s; sometimes transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s and active amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
s are included.
Ear background
The ear of the typical mammal consists of three parts. The outer earOuter ear
The outer ear is the external portion of the ear, which consists of the pinna, concha, and external auditory meatus. It gathers sound energy and focuses it on the eardrum . One consequence of the configuration of the external ear is to selectively boost the sound pressure 30- to 100-fold for...
collects sounds like a horn and guides them to the eardrum
Eardrum
The eardrum, or tympanic membrane, is a thin membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles...
. Vibrations of the drum are conveyed to the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
via a system of bones called ossicles
Ossicles
The ossicles are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth . The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss...
. These leverage the larger motions of the eardrum
Eardrum
The eardrum, or tympanic membrane, is a thin membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles...
to the smaller vibrations of the oval window
Oval window
The oval window is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear.Vibrations that come into contact with the tympanic membrane travel through the three ossicles and into the inner ear...
. This window connects to the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
which is a long dual channel arrangement consisting of two channels separated by the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
. The structure, about 36 mm in length, is coiled to conserve space. The oval window
Oval window
The oval window is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear.Vibrations that come into contact with the tympanic membrane travel through the three ossicles and into the inner ear...
introduces sounds to the upper channel. The lower channel has a round window
Round window
The round window is one of the two openings into the inner ear. It is closed off from the middle ear by the round window membrane, which vibrates with opposite phase to vibrations entering the inner ear through the oval window...
but this is not driven by the bones of the middle ear. The far end of the structure has a hole between the two channels called the helicotrema
Helicotrema
The helicotrema is the part of the cochlear labyrinth where the scala tympani and the scala vestibuli meet. It is the main component of the cochlear apex. The hair cells in this area best detect low frequency sounds.-External links:* at Allegheny University of the Health Sciences* at IUPUI...
that equalizes slowly varying pressures in the two channels. A series of sensory hair cells along the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
respond to send neural pulses towards the brain.
Ear modeling
Models for the ear of a direct kind have been created, most notably by (Nobel Laureate) Georg von BekesyGeorg von Békésy
Georg von Békésy was a Hungarian biophysicist born in Budapest, Hungary.In 1961, he was awarded the Nobel Prize in Physiology or Medicine for his research on the function of the cochlea in the mammalian hearing organ.-Research:Békésy developed a method for dissecting the inner ear of human...
. He used glass slides, razor blades, and an elastic membrane to represent the helicotrema
Helicotrema
The helicotrema is the part of the cochlear labyrinth where the scala tympani and the scala vestibuli meet. It is the main component of the cochlear apex. The hair cells in this area best detect low frequency sounds.-External links:* at Allegheny University of the Health Sciences* at IUPUI...
. He could measure vibrations along the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
in response to different excitations frequencies. He found that the pattern of displacements for given frequency sine wave along the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
rose somewhat gradually to a peak and thereafter fell. High frequencies favored shorter distances from the oval window
Oval window
The oval window is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear.Vibrations that come into contact with the tympanic membrane travel through the three ossicles and into the inner ear...
than did lower ones. Frequency values approximate a logarithmic distribution with distance.
Detailed discussions of the direct models by von Bekesy will be found in his book, "Experiments in Hearing", McGraw-Hill, 1960. Also see his article and others in S. S. Stevens, "Handbook of Experimental Psychology", John Wiley and Sons, 1951. This handbook is singled out as a major source of information on speech and hearing, word recognition, and other topics as well as data on the human ear.
Mechanical and electrical analogs
Early mechanical and electrical analog ears were recounted in the 1954 book Analog Methods in Computation and Simulation:A direct (mechanical) model uses the variables of air and water pressure, fluid velocity and viscosity, and displacement. An electrical analog model uses a different set of variables, namely, voltage and current. The outer and middle parts of the ear can be represented with a collection of coils, capacitors, and an ideal transformer to represent the leveraging effect of the ossicles
Ossicles
The ossicles are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth . The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss...
. This circuit terminates with a capacitor representing the oval window
Oval window
The oval window is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear.Vibrations that come into contact with the tympanic membrane travel through the three ossicles and into the inner ear...
. From there, the two channels are represented with a sequence of inductors and resistors for fluid flow within each channel with the two channels joined with a sequence of series resonant RLC circuits. Voltages across capacitances represent basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
displacements. Element values along the cochlea are tapered in a logarithmic fashion to represent lowering frequency responses with distance.
The pattern of voltages along the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
can be viewed on an oscilloscope. Average values can be obtained with rectification and shown as patterns using a high speed commutator. The analog ear shows patterns that closely follow those observed by Georg von Békésy
Georg von Békésy
Georg von Békésy was a Hungarian biophysicist born in Budapest, Hungary.In 1961, he was awarded the Nobel Prize in Physiology or Medicine for his research on the function of the cochlea in the mammalian hearing organ.-Research:Békésy developed a method for dissecting the inner ear of human...
on his more direct model.
The first relatively complete model was constructed in the early 1960s at the University of Arizona by two graduate students and their faculty mentor with support from the newly established Air Force Bionics
Bionics
Bionics is the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology.The word bionic was coined by Jack E...
program. This work was first summarized in a report: "An Electronic Analog of the Ear", Technical Documentary Report No. AMRL
Armored Medical Research Laboratory
The Armored Medical Research Laboratory was a U.S. Army medical research facility maintained at Fort Knox, KY from 1942 to 1961 to solve environmental problems encountered by soldiers in tanks.-Mission:...
-TDR
Technical documentation
In engineering, technical documentation refers to any type of documentation that describes handling, functionality and architecture of a technical product or a product under development or use.Documentation may include:* patents...
-63-60, June, 1963, Biophysics Laboratory, 6570-th Aerospace Medical Research Laboratories, Aerospace Medical Division, Air Force Systems Command, by E. Glaesser, W. F. Caldwell, and J. L. Stewart. The report contains an extensive list of references. The work was also reported at Bionics
Bionics
Bionics is the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology.The word bionic was coined by Jack E...
symposia.
John L. Stewart and Covox
Unlike models based on a series of active filters or represented with digital equations, an analog ear can incorporate nonlinearities that represent nonlinear actions of the basilar membraneBasilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
, perhaps caused by non-symmetric motions of sensory cells resulting in non-symmetric motions of the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
. Difference frequencies could be generated as are observed in the human. Some difference frequencies originating in the cochela can be observed in the outer ear
Outer ear
The outer ear is the external portion of the ear, which consists of the pinna, concha, and external auditory meatus. It gathers sound energy and focuses it on the eardrum . One consequence of the configuration of the external ear is to selectively boost the sound pressure 30- to 100-fold for...
.
Neural signals responding to motions of the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
show responses in one direction as in rectification. At all but low frequencies, the neural measure averages over multiple cycles to give the equivalent of rectification followed by averaging (low-pass filtering). Over the entire cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
, response shows as a pattern that varies more slowly that the applied frequency but that does follow the envelope of the applied signal. Each group of cells can give rise to a semi-periodic wave that can be analyzed by neurons in the brain. The total pattern that arises from a sound can thus be thought of as a two-dimensional pattern in time with one axis being the distance along the basilar membrane
Basilar membrane
The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani .-Function:...
and the other being distance along some sequence of neurons. These patterns, varying at rates less than lower audio frequencies, have shapes that can be identified much like patterns in vision. The concept of the "neural analyzer" as an extension of cochlear patterns is discussed in U. S. patent 3,387,093, "Speech Bandwidth Compression System", June 4, 1968. (Filed in 1964.)
It was found that the analog ear with its asymmetric overlapping bands was more reliable in identifying speech sounds that is a conventional frequency spectrum
Frequency spectrum
The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency.Any signal...
. The second formant is the most significant single measure. Speech sounds of interest include whispered
Whispered
The Whispered are unique individuals in the Full Metal Panic! universe who possess access to Black Technology, technology that outstrips the level of technology that should exist in the world.- Abilities :...
and clipped speech. See "Speech Processing with A Cochlear-Neural Analog, John L. Stewart, 1967, Technical Documentary Report No. AMRL
Armored Medical Research Laboratory
The Armored Medical Research Laboratory was a U.S. Army medical research facility maintained at Fort Knox, KY from 1942 to 1961 to solve environmental problems encountered by soldiers in tanks.-Mission:...
-TR
Technical report
A technical report is a document that describes the process, progress, or results of technical or scientific research or the state of a technical or scientific research problem. It might also include recommendations and conclusions of the research...
-66-229. An article published in the journal Behavioral Science studied constraints to sensory discrimination imposed by two kinds of neural noise. Considerable information on speech patterns and recognition is reported by a number of different authors in the "Handbook of Experimental Psychology" referred to above.
Applications were made to animals and insects with appropriate ear models. See "Aural Systems Simulation for Birds and Insects," Robert L. Lucas, John L. Stewart, and Richard A. Schaeffer. Technical Report AFAL-TR-66-12. January, 1966. Another study using the analog ear was "Simulating Mechanisms in Animal Echoranging," John L. Stewart and James M. Kasson. Technical Report AMRL
Armored Medical Research Laboratory
The Armored Medical Research Laboratory was a U.S. Army medical research facility maintained at Fort Knox, KY from 1942 to 1961 to solve environmental problems encountered by soldiers in tanks.-Mission:...
-TR
Technical report
A technical report is a document that describes the process, progress, or results of technical or scientific research or the state of a technical or scientific research problem. It might also include recommendations and conclusions of the research...
-68-194. September, 1969.
Many reports, articles, and patents followed the research as cited in the reports listed here. The last full report employed a relatively early version of a computer program written in time-shared BASIC
BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
. See "A Theory and Physical Model for Cochlear Mechanics," John L. Stewart. Acta Oto-Laryngologica, Supplement 294, 1972. Parameters of the analog ear and patterns obtained with the computer program are shown. Patterns and parameters given in this report are sufficient to reproduce analog ears.
Stewart also self-published several books, doing business as Santa Rita Technology, and later as Covox, including The Analog Ear Story and The Analog Ear–brain System in 1964, and The Bionic Ear in 1979.http://books.google.com/books?q=inauthor%3Ajohn+inauthor%3Astewart+intitle%3Aear
The research resulting from analog ear studies fueled the creation of special sounds for use in repelling birds and other pests. Sounds were synthesized to follow natural bird calls but were of a switching kind. The concept is similar to the use of a babble of human voices for jamming another person's communications. The "Av-Alarm" was the principal product. It was also adapted to the transonic and ultrasonic regions with a device called "Transonic."
The research also led to development of an early speech word recognizer that operated with 8-bit computers as well as later ones based on 16 bit processors. The product line was developed by Covox, Inc. with product names of "Speech Thing" and "Voice Master."
A number of U.S. (and foreign) patents on topics related to Stewart's analog ear were granted. In the order of filing dates starting in 1962, numbers are 3,294,909, 3,325,597, 3,387,093, 3,432,618, 3,378,700, 3,483,325, 3,459,034, 3,543,138, and 3,510,588.