Patent US5245665A successfully refreshed from Google Patents.
US5245665A
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Method and apparatus for adaptive audio resonant frequency filtering
Assignee: Sabine Musical Manufacturing Co Inc
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Filing: 1991-06-12
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Granted: 1993-09-14
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Expires: 2011-06-12
Abstract
Abstract Audio signals are digitized and an FFT is conducted on samples of the digitized signals to produce corresponding frequency spectrums. These spectrums are analyzed, such as by determining one or more peak frequency magnitudes which are 33 dB greater than harmonics or subharmonics of the frequency in a plurality of several successive spectrums, to detect resonating feedback frequencies. The offending frequency is then filtered in the time domain, either in the digitized form or analog form, to eliminate the feedback.
Inventors
- 👤 Michael P. Lewis
- 👤 Timothy J. Tucker
- 👤 Doran M. Oster
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 11:45
CPC Classifications
H; H04; H04R; H04R3/00; H04R3/02
Claims Analysis
Total Claims: 60
Claim 1
Independent Claim
257 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising analog-to-digital convertor means for digitizing the electrical signals and for periodically producing a predetermined series of digital signals corresponding to a predetermined time segment of the electrical signals; computer means including fast Fourier transform means for converting each series of digital signals into a frequency spectrum, means for examining successive frequency spectrums to determine the presence of an undesirable acoustic feedback, and means for generating frequency specific filter control signals in response to the determination of the presence of the undesirable acoustic feedback; the frequency spectrum examining means including means for determining a maximum magnitude frequency, mean for determining whether a magnitude of the maximum magnitude frequency is greater than a magnitude of a selected harmonic of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency, and means for determining the presence of a candidate resonant frequency in a plurality of a predetermined number of successive spectrums to indicate the candidate resonant frequency as the undesirable acoustic feedback; and filter means controlled by the filter control signals form the computer means for attenuating one or more narrow frequency bands in the electrical signal to eliminate the undesirable acoustic feedback.
Claim 2
Independent Claim
257 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising analog-to-digital convertor means for digitizing the electrical signals and for periodically producing a predetermined series of digital signals corresponding to a predetermined time segment of the electrical signals; computer means including fast Fourier transform means for converting each series of digital signals into a frequency spectrum, means for examining successive frequency spectrums to determine the presence of an undesirable acoustic feedback, and means for generating frequency specific filter control signals in response to the determination of the presence of the undesirable acoustic feedback; the frequency spectrum examining means including means for determining a maximum magnitude frequency, mean for determining whether a magnitude of the maximum magnitude frequency is greater than a magnitude of a selected harmonic of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency, and means for determining the presence of a candidate resonant frequency in a plurality of a predetermined number of successive spectrums to indicate the candidate resonant frequency as the undesirable acoustic feedback; and filter means controlled by the filter control signals form the computer means for attenuating one or more narrow frequency bands in the electrical signal to eliminate the undesirable acoustic feedback.
Claim 3
Dependent Claim
69 words
An apparatus as claimed in claim 1 wherein the frequency spectrum examining means includes means for determining a plurality of largest magnitude frequencies, and means for determining whether a magnitude of each of the largest magnitude frequencies is greater than a magnitude of a selected harmonic of each respective largest magnitude frequency by at least a predetermined factor to indicate each largest magnitude frequency as a candidate resonant frequency.
Claim 4
Dependent Claim
19 words
An apparatus as claimed in claim 1 wherein the predetermined factor is equal to or greater than 20 decibels.
Claim 5
Dependent Claim
19 words
An apparatus as claimed in claim 1 wherein the predetermined factor is equal to or greater than 33 decibels.
Claim 6
Dependent Claim
85 words
An apparatus as claimed in claim 1 wherein the means for determining whether the magnitude of the maximum magnitude frequency is greater than the magnitude of a selected harmonic of the maximum magnitude frequency by at least a predetermined factor includes means for determining whether the magnitude of the maximum magnitude frequency is greater than a magnitude of a first and second higher harmonics and a first subharmonic of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency.
Claim 7
Dependent Claim
15 words
An apparatus as claimed in claim 1 wherein the predetermined number is at least three.
Claim 8
Dependent Claim
15 words
An apparatus as claimed in claim 6 wherein the predetermined number is at least five.
Claim 9
Dependent Claim
45 words
An apparatus as claimed in claim 1 wherein the means for determining the presence of a candidate resonant frequency determines the presence of a candidate resonant frequency in at least three of five successive spectrums to indicate the candidate resonant frequency as a resonant frequency.
Claim 10
Dependent Claim
70 words
An apparatus as claimed in claim 1 wherein the filter means includes (a) second computer means which includes means for receiving both the digitized signals from the analog-to-digital convertor mean and the control signals from a first computer means, digital filter means for attenuating one or more narrow bands of frequencies in the digital signals; and (b) digital-to-analog convertor means for converting ht filter digital signals into filtered analog signals.
Claim 11
Dependent Claim
80 words
An apparatus as claimed in claim 1 wherein the fast Fourier transform is performed with a first resolution in a low frequency range from a minimum audio frequency to a middle audio frequency and is performed with a second resolution in a high frequency range form the middle audio frequency at a maximum audio frequency, said first resolution being in a range from 1 to 3 Hertz and said second resolution being in a range from 5 to 30 Hertz.
Claim 12
Dependent Claim
30 words
An apparatus as claimed in claim 10 wherein the fast Fourier transform for the low frequency range is performed with one-hal for less of the predetermined series of digital signals.
Claim 13
Dependent Claim
40 words
An apparatus as claimed in claim 10 wherein successive pluralities of the predetermined series of digital signals are averaged to generate a series of average digital signals upon which the fast Fourier transform for the low frequency range is performed.
Claim 14
Dependent Claim
53 words
An apparatus as claimed in claim 1 in which the computer means includes software means for identifying a first preselected number of resonant feedback frequencies which are indicative of natural acoustics in an area in which the apparatus is placed and for controlling the filter means to continuously attenuate said preselected resonant frequencies.
Claim 15
Dependent Claim
32 words
An apparatus as claimed in claim 1 wherein the computer means upon indicating a resonant feedback frequency generates control signals to increase the attenuation of the resonant frequency by a predetermined amount.
Claim 16
Dependent Claim
98 words
An apparatus as claimed in claim 1 wherein the computer means includes setup means which in turn includes means for generating a flat frequency spectrum, means for converting the flat frequency spectrum into a digitized time domain time segment, digital-to-analog convertor means for generating an analog signal from the digitized time segment, means for applying the analog signal to the speaker, means for receiving and analyzing the electrical signal from the microphone to identify any resonant feedback frequencies, and means responsive to the receiving and analyzing mean for setting up filters to attenuate any such resonant feedback frequencies.
Claim 17
Dependent Claim
23 words
An apparatus as claimed in claim 1 wherein the filter means includes a plurality of analog notch filters operating on the electrical signal.
Claim 18
Dependent Claim
68 words
An apparatus as claimed in claim 1 wherein the means for determining whether the magnitude of the maximum magnitude frequency is greater than the magnitude of as elected harmonic comprises means for determining whether the magnitude of the maximum frequency is greater than the magnitudes of a plurality of selected harmonics of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency.
Claim 19
Dependent Claim
70 words
An apparatus as claimed in claim 17 wherein the frequency spectrum examining means includes means for determining a plurality of largest magnitude frequencies, and means for determining whether a magnitude of each of the large magnitude frequencies is greater than magnitudes of a plurality of selected harmonics of each respective largest magnitude frequency by at least a predetermined factor to indicate each largest magnitude frequency as a candidate resonant frequency.
Claim 20
Dependent Claim
19 words
An apparatus as claimed in claim 17 wherein the predetermined factor is equal to or greater than 20 decibels.
Claim 21
Dependent Claim
19 words
An apparatus as claimed in claim 17 wherein the predetermined factor is equal to or greater than 33 decibels.
Claim 22
Dependent Claim
69 words
An apparatus as claimed in claim 1 wherein the means for determining whether the magnitude of the maximum magnitude frequency is greater than the magnitude of a selected harmonic comprises means for determining whether the magnitude of the maximum frequency is greater than magnitudes of a selected harmonic and a selected subharmonic of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency.
Claim 23
Dependent Claim
72 words
An apparatus as claimed in claim 21 wherein the frequency spectrum examining means includes means for determining a plurality of largest magnitude frequencies, and means for determining whether a magnitude of each of the largest magnitude frequencies is greater than magnitudes of a selected harmonic and a selected subharmonic of each respective largest magnitude frequency by at least a predetermined factor to indicate each largest magnitude frequency as a candidate resonant frequency.
Claim 24
Dependent Claim
25 words
An apparatus as claimed in claim 1 wherein the filter means attenuates one or more frequency bands having widths less than one-fourth of an octave.
Claim 25
Dependent Claim
26 words
An apparatus as claimed in claim 23 wherein the frequency band or bands being attenuated have widths equal to or less than one-tenth of an octave.
Claim 26
Independent Claim
254 words
A method of eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the method comprising periodically digitizing a time segment of a predetermined duration of the electrical signals to produce a plurality of series of digital signals; converting by a fast Fourier transform algorithm in computer means each of the plurality of series of digital signals into a frequency spectrum; examining the frequency spectrums by the computer means to determine the presence of an undesirable acoustic feedback; the examining of the frequency spectrums including determining a maximum magnitude frequency, determining whether a magnitude of the maximum magnitude frequency is greater than a magnitude of a selected harmonic of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency, and determining the presence of a candidate resonant frequency in a plurality of a predetermined number of successive spectrums to indicate the candidate resonant frequency as the undesirable acoustic feedback; generating frequency specific filter control signals by the computer means in response to the determination of the presence of the undesirable acoustic feedback; and attenuating one or more narrow frequency bands in the electric signal by controlling filter means by the filter control signals from the computer means to eliminate the undesirable acoustic feedback.
Claim 27
Independent Claim
254 words
A method of eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the method comprising periodically digitizing a time segment of a predetermined duration of the electrical signals to produce a plurality of series of digital signals; converting by a fast Fourier transform algorithm in computer means each of the plurality of series of digital signals into a frequency spectrum; examining the frequency spectrums by the computer means to determine the presence of an undesirable acoustic feedback; the examining of the frequency spectrums including determining a maximum magnitude frequency, determining whether a magnitude of the maximum magnitude frequency is greater than a magnitude of a selected harmonic of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency, and determining the presence of a candidate resonant frequency in a plurality of a predetermined number of successive spectrums to indicate the candidate resonant frequency as the undesirable acoustic feedback; generating frequency specific filter control signals by the computer means in response to the determination of the presence of the undesirable acoustic feedback; and attenuating one or more narrow frequency bands in the electric signal by controlling filter means by the filter control signals from the computer means to eliminate the undesirable acoustic feedback.
Claim 28
Dependent Claim
89 words
A method as claimed in claim 25 wherein said attenuation of one or more narrow frequency bands in the electrical signal is performed by digitizing the electrical signals, passing the digitized electrical signals to second computer means, passing the control signals from a first computer means to the second computer means, attenuating one or more narrow bands of frequencies in the digital signals by digital filter means in the second computer means in accordance with the filter control signals, and converting the attenuated digital signals into filtered analog signals.
Claim 29
Independent Claim
228 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising analog-to-digital convertor means for digitizing the electrical signals from the microphone; first and second microcomputers for receiving digitized electrical signals; said first microcomputer including means for receiving the digitized signals from the analog-to-digital convertor means, means for examining the digitized electrical signals to determine the presence of an undesirable acoustic feedback, means for generating frequency specific filter control signals in response to the determination of the presence of the undesirable acoustic feedback, and means for transmitting the digitized signals along with the frequency specific control signals; said second microcomputer including means for receiving the digitized signals along with the frequency specific filter control signals from the first microcomputer, and filter means controlled by the filter control signals for attenuating one or more narrow frequency bands in the digitized electrical signals to produce filtered digitized electrical signals from which the undesirable acoustic feedback is eliminated; and digital-to analog convertor means for converting the filtered digitized electrical signals into filtered analog signals for driving said amplified and said speaker.
Claim 30
Independent Claim
228 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising analog-to-digital convertor means for digitizing the electrical signals from the microphone; first and second microcomputers for receiving digitized electrical signals; said first microcomputer including means for receiving the digitized signals from the analog-to-digital convertor means, means for examining the digitized electrical signals to determine the presence of an undesirable acoustic feedback, means for generating frequency specific filter control signals in response to the determination of the presence of the undesirable acoustic feedback, and means for transmitting the digitized signals along with the frequency specific control signals; said second microcomputer including means for receiving the digitized signals along with the frequency specific filter control signals from the first microcomputer, and filter means controlled by the filter control signals for attenuating one or more narrow frequency bands in the digitized electrical signals to produce filtered digitized electrical signals from which the undesirable acoustic feedback is eliminated; and digital-to analog convertor means for converting the filtered digitized electrical signals into filtered analog signals for driving said amplified and said speaker.
Claim 31
Dependent Claim
61 words
An apparatus as claimed in claim 27 wherein the means for examining the digitized electrical signals includes means for determining the presence of a frequency component in the digitized electrical signals having a magnitude which exceeds by at least twenty decibels a magnitude of each of a plurality of selected harmonic frequency components in the digitized signals for a substantial duration.
Claim 32
Dependent Claim
62 words
An apparatus as claimed in claim 27 wherein the means for examining the digitized electrical signals includes means for determining the presence of a frequency component in the digitized electrical signals having a magnitude which exceeds by at least twenty decibels each of a selected harmonic frequency component and a selected subharmonic frequency component in the digitized signals for a substantial duration.
Claim 33
Independent Claim
156 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising means for sensing in the electrical signals from the microphone the presence of a frequency component having ga magnitude which exceeds by at least twenty decibels the magnitudes of each of a plurality of selected harmonic components in the electrical signals for a substantial duration to determine a resonating feedback frequency component; and filer means controlled by the sensing means for attenuating said resonating feedback frequency component in the electrical signals from the microphone to produce filtered electrical signals from which the resonating feedback frequency component is eliminated for driving said amplifier and said speaker.
Claim 34
Independent Claim
156 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising means for sensing in the electrical signals from the microphone the presence of a frequency component having ga magnitude which exceeds by at least twenty decibels the magnitudes of each of a plurality of selected harmonic components in the electrical signals for a substantial duration to determine a resonating feedback frequency component; and filer means controlled by the sensing means for attenuating said resonating feedback frequency component in the electrical signals from the microphone to produce filtered electrical signals from which the resonating feedback frequency component is eliminated for driving said amplifier and said speaker.
Claim 35
Dependent Claim
152 words
An apparatus as claimed in claim 30 wherein the sensing means comprises analog-to-digital convertor means for digitizing the electrical signals to produce a plurality of series of digital signals corresponding to time segments of the electrical signals; and computer means including fast Fourier transform means for transforming each of the plurality of series of digital signals to produce a plurality of frequency spectrums, means for determining a plurality of a largest magnitude frequency components in each of the frequency spectrums and for indicating as a candidate resonant frequency each of the determined largest magnitude frequency components having a magnitude exceeding by at least twenty decibels magnitudes of a plurality of selected harmonics of the corresponding determined largest magnitude frequency component, and means responsive to a candidate resonant frequency being present in a predetermined number of the plurality of frequency spectrums for indicating such candidate resonant frequency as a resonating feedback frequency component.
Claim 36
Dependent Claim
88 words
An apparatus as claimed in claim 30 wherein the filter means comprise analog-to-digital convertor means for digitizing the electrical signals from the microphone, computer means for receiving the digitized electrical signals, and digital-to-analog convertor means for converting filtered digitized electrical signals from the computer means to analog electrical signals for driving said amplifier and said speaker, said computer means including a digital filter algorithm for attenuating a narrow bandwidth of frequencies including said resonating frequency component in the digitized electrical signals to produce the filtered digitized electrical signals.
Claim 37
Dependent Claim
80 words
An apparatus as claimed in claim 31 wherein the filter means comprises second computer means for receiving the digitized electrical signals, and digital-to-analog convertor means for converting filtered digitized electrical signals from the second computer means to analog electrical signals for driving said amplifier and said speaker, said second computer means including a digital filter algorithm for attenuating a narrow bandwidth of frequencies including said resonating frequency component in the digitized electrical signals to produce the filtered digitized electrical signals.
Claim 38
Dependent Claim
25 words
An apparatus as claimed in claim 30 wherein the filter means attenuates one or more frequency band having widths less than one-fourth of an octave.
Claim 39
Dependent Claim
26 words
An apparatus as claimed in claim 34 wherein the frequency band or bands being attenuated have widths equal to or less than one-tenth of an octave.
Claim 40
Dependent Claim
40 words
An apparatus as claimed in claim 30 wherein the sensing means must sense a magnitude of a frequency component exceeding by thirty-three or more decibels the magnitudes of the plurality of selected harmonics to determine a resonating feedback frequency component.
Claim 41
Independent Claim
256 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising analog-to-digital convertor mean for digitizing the electrical signals and for periodically producing a predetermined series of digital signals corresponding to a predetermined time segment of the electrical signals; computer means including fast Fourier transform means for converting each series of digital signals into a frequency spectrum, means for examining successive frequency spectrums to determine the presence of an undesirable acoustic feedback, and means for generating frequency specific filter control signals in response to the determination of the presence of the undesirable acoustic feedback; the frequency spectrum examining mean including means for determining a maximum magnitude frequency, means for determining whether a magnitude of the maximum magnitude frequency is greater than a magnitude of as elected subharmonic of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency, and means for determining the presence of a candidate resonant frequency in a plurality of a predetermined number of successive spectrums to indicate the candidate resonant frequency as the undesirable acoustic feedback; and filter means controlled the filter control signals from the computer means for attenuating one or more narrow frequency bands in the electric signal to eliminate the undesirable acoustic feedback.
Claim 42
Independent Claim
256 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising analog-to-digital convertor mean for digitizing the electrical signals and for periodically producing a predetermined series of digital signals corresponding to a predetermined time segment of the electrical signals; computer means including fast Fourier transform means for converting each series of digital signals into a frequency spectrum, means for examining successive frequency spectrums to determine the presence of an undesirable acoustic feedback, and means for generating frequency specific filter control signals in response to the determination of the presence of the undesirable acoustic feedback; the frequency spectrum examining mean including means for determining a maximum magnitude frequency, means for determining whether a magnitude of the maximum magnitude frequency is greater than a magnitude of as elected subharmonic of the maximum magnitude frequency by at least a predetermined factor to indicate a candidate resonant frequency, and means for determining the presence of a candidate resonant frequency in a plurality of a predetermined number of successive spectrums to indicate the candidate resonant frequency as the undesirable acoustic feedback; and filter means controlled the filter control signals from the computer means for attenuating one or more narrow frequency bands in the electric signal to eliminate the undesirable acoustic feedback.
Claim 43
Dependent Claim
69 words
An apparatus as claimed in claim 37 wherein the frequency spectrum examining means includes mean for determining a plurality of largest magnitude frequencies, and means for determining whether a magnitude of each of the largest magnitude frequencies is greater than a magnitude of a selected subharmonic of each respective largest magnitude frequency by at least a predetermined factor to indicate each largest magnitude frequency as a candidate resonant frequency.
Claim 44
Dependent Claim
19 words
An apparatus as claimed in claim 37 wherein the predetermined factor is equal to or greater than 20 decibels.
Claim 45
Dependent Claim
19 words
An apparatus as claimed in claim 37 wherein the predetermined factor is equal to or greater than 33 decibels.
Claim 46
Independent Claim
159 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising means for sensing in the electrical signals from the microphone the presence of a frequency component having the magnitude which exceeds by at least twenty decibels magnitudes of each of a selected harmonic component and a selected subharmonic component in the electrical signals for a substantial duration to designate the frequency component as an undesirable acoustic feedback; and filter means controlled by the sensing means for attenuating said undesirable acoustic feedback in the electrical signals from the microphone to produce filtered electrical signals from which said undesirable acoustic feedback is eliminated for driving said amplifier and said speaker.
Claim 47
Independent Claim
159 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising means for sensing in the electrical signals from the microphone the presence of a frequency component having the magnitude which exceeds by at least twenty decibels magnitudes of each of a selected harmonic component and a selected subharmonic component in the electrical signals for a substantial duration to designate the frequency component as an undesirable acoustic feedback; and filter means controlled by the sensing means for attenuating said undesirable acoustic feedback in the electrical signals from the microphone to produce filtered electrical signals from which said undesirable acoustic feedback is eliminated for driving said amplifier and said speaker.
Claim 48
Dependent Claim
152 words
An apparatus as claimed in claim 41 wherein the sensing means comprises analog-to-digital convertor means for digitizing the electrical signals to produce a plurality of series of digital signals corresponding to time segments of the electrical signals; and computer means including fast Fourier transform means for transforming each of the plurality of series of digital signals to produce a plurality of frequency spectrums, means for determining a plurality of largest magnitude frequency components in each of the frequency spectrums and for indicating as a candidate resonant frequency each of the determined largest magnitude frequency components having a magnitude exceeding by at least twenty decibels magnitudes of a selected harmonic and a selected subharmonic of the corresponding determined largest magnitude frequency component, and means responsive to a candidate resonant frequency being presenting a predetermined number of the plurality of frequency spectrums for indicating such candidate resonant frequency as a resonating feedback frequency component.
Claim 49
Dependent Claim
88 words
An apparatus as claimed in claim 41 wherein the filter means comprises analog-to-digital convertor means for digitizing the electrical signals from the microphone, computer means for receiving the digitized electrical signals, and digital-to-analog convertor means for converting filtered digitized electrical signals from the computer means to analog electrical signals for driving said amplifiers and said speaker, said computer means including a digital filter algorithm for attenuating a narrow bandwidth of frequencies including said resonating frequency component in the digitized electrical signal to produce the filtered digitized electrical signals.
Claim 50
Dependent Claim
80 words
An apparatus as claimed in claim 40 wherein the filter means comprises second computer means for receiving the digitized electrical signals, and digital-to-analog convertor means for converting filtered digitized electrical signals from the second computer means to analog electrical signal for driving said amplifier and said speaker, said second computer means including a digital filter algorithm for attenuating a narrow bandwidth of frequencies including said resonating frequency component in the digitized electrical signals to produce the filtered digitized electrical signals.
Claim 51
Independent Claim
152 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising means for sensing the presence of an acoustical frequency component having a magnitude which exceeds by at least twenty decibels a magnitude of a selected harmonic of the acoustical component for a substantial duration to designate the acoustical frequency component as an undesirable acoustic feedback; and filter means controlled by the sensing means for attenuating a narrow bandwidth encompassing the designated undesirable acoustic feedback in the electrical signals from the microphone to produce filtered electrical signals from which the undesirable acoustic feedback is eliminated for driving said amplifier and said speaker.
Claim 52
Independent Claim
152 words
An apparatus for eliminating acoustical feedback in a system which includes a microphone for converting audible acoustic signals into electrical signals, an amplifier for amplifying the electrical signals from the microphone, and a speaker for converting the amplified electrical signals into amplified audible acoustic signals and for broadcasting the amplified acoustic signals in the vicinity of the microphone, the apparatus comprising means for sensing the presence of an acoustical frequency component having a magnitude which exceeds by at least twenty decibels a magnitude of a selected harmonic of the acoustical component for a substantial duration to designate the acoustical frequency component as an undesirable acoustic feedback; and filter means controlled by the sensing means for attenuating a narrow bandwidth encompassing the designated undesirable acoustic feedback in the electrical signals from the microphone to produce filtered electrical signals from which the undesirable acoustic feedback is eliminated for driving said amplifier and said speaker.
Claim 53
Dependent Claim
150 words
An apparatus as claimed in claim 45 wherein the sensing means comprises analog-to-digital convertor means for digitizing electrical signals to produce a plurality of series of digital signals corresponding to time segments of the electrical signals; and computer means including fast Fourier transform means for transforming each of the plurality of series of digital signals to produce a plurality of frequency spectrums, means for determining a plurality of largest magnitude frequency components in each of the frequency spectrums and for indicating as a candidate resonant frequency each of the determined largest magnitude frequency components having a magnitude exceeding by at least twenty decibels magnitudes of a plurality of selected harmonics of the corresponding determined largest magnitude frequency component, and means responsive to a candidate resonant frequency being present in a predetermined number of the plurality of frequency spectrums for indicating such candidate resonant frequency as a resonating feedback frequency component.
Claim 54
Dependent Claim
88 words
An apparatus as claimed in claim 45 wherein the filter means comprises analog-to-digital convertor means for digitizing the electrical signals from the microphone, computer means for receiving the digitized electrical signals, and digital-to-analog convertor means for converting filtered digitized electrical signals from the computer means to analog electrical signals for driving said amplified and said speaker, said computer means including a digital filter algorithm for attenuating a narrow bandwidth of frequencies including said resonating frequency component in the digitized electrical signals to produce the filtered digitized electrical signals.
Claim 55
Dependent Claim
80 words
An apparatus as claimed in claim 46 wherein the filter means comprises second computer means for receiving the digitized electrical signals, and digital-to-analog convertor means for converting filtered digitized electrical signals from the second computer means to analog electrical signals for driving said amplifier and said speaker, said second computer means including a digital filer algorithm for attenuating a narrow bandwidth of frequencies including said resonating frequency component in the digitized electrical signals to produce the filtered digitized electrical signals.
Claim 56
Dependent Claim
25 words
An apparatus as claimed in claim 45 wherein the filter means attenuates one or more frequency bands having widths less than one-tenth of an octave.
Claim 57
Dependent Claim
38 words
An apparatus as claimed in claim 45 wherein the sensing means must sense a magnitude of a frequency component exceeding by thirty-three or more decibels the magnitude of a selected harmonic to determine a resonating feedback frequency component.
Claim 58
Dependent Claim
53 words
An apparatus as claimed in claim 45 wherein the sensing means senses the presence of a frequency component having a magnitude which exceeds by at least twenty decibels magnitudes of each of a plurality of selected harmonic components in the electrical signals for a substantial duration to determine a resonating feedback frequency component.
Claim 59
Dependent Claim
25 words
An apparatus as claimed in claim 45 wherein the selected harmonic is a 1.5 harmonic, a first harmonic, a second harmonic or a first subharmonic.
Claim 60
Dependent Claim
27 words
An apparatus as claimed in claim 46 wherein the plurality of selected harmonics include a 1.5 harmonic, a first harmonic, a second harmonic and a first subharmonic.
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| 3.5 Years (Year 4) | 1996-09-13 | 1997-03-15 | 1997-09-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2000-09-13 | 2001-03-15 | 2001-09-14 | $3760.00 | Window Closed / Lapsed |
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