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US 4,232,192 AGranted
Moving-average notch filter
AssigneeStarkey Labs, Inc.
InventorAloysius A. Beex
Life of this patent
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Abstract
A moving-average notch filter with a well-defined phase characteristic for use in eliminating oscillation frequencies in a sound amplification system, wherein this moving-average filter is designed to have an output Y.sub.K in accordance with the system equation ##EQU1## where b.sub.1 are the weighting coefficients, X.sub.K-i are input samples, and K is a constant. This filter may be designed to have a linear phase characteristic. In one embodiment, the location of the notch in the frequency response of the filter may be made to automatically track the drift of an acoustic oscillation frequency.
Claims19
A sound amplification system comprising:
- first transducer means for providing a signal in accordance with sound-wave excitations in the environment;
- amplification means for amplifying said signal;
- filter means having a notch therein corresponding to an oscillation frequency of said signal which is to be suppressed;
- and
- second transducer means for converting the output from the filter means into excitations detectable by a listener,
- wherein the improvement comprises said filter means being a moving-average filter means having a frequency response with at least one notch therein, the output Y.sub.K of said moving-average filter being derived in accordance with the system equation ##EQU9## wherein the b's are weighting coefficients, the X's are input samples from said amplification means, S and K are constants, and each output Y.sub.K is composed of M+1 samples, and wherein the phase characteristic of said moving-average filter means is well-defined in the vicinity of and at said notch to limit the number of possible oscillation frequencies at the notch to a finite number,
- wherein said moving-average filter means further comprises:
- clock means for generating a clock signal;
- memory means for sampling the output from said amplification means in accordance with said clock signal and for storing and shifting at least M+1 samples in accordance with said clock signal;
- and
- automatic clock control means for controlling the frequency of said clock signal in accordance with the output from said moving-average filter means to thereby control the location of said at least one notch in the frequency response of said moving-average filter means.
8 more elements
A sound amplification system comprising:
- first transducer means for providing a signal in accordance with sound-wave excitations in the environment;
- amplification means for amplifying said signal;
- filter means having a notch therein corresponding to an oscillation frequency of said signal which is to be suppressed;
- and
- second transducer means for converting the output from the filter means into excitations detectable by a listener,
- wherein the improvement comprises said filter means being a moving-average filter means having a frequency response with at least one notch therein, the output Y.sub.K of said moving-average filter being derived in accordance with the system equation ##EQU10## wherein the b's are weighting coefficients, the X's are input samples from said amplification means, S and K are constants, and each output Y.sub.K is composed of M+1 samples, and wherein the phase characteristic of said moving-average filter means is well-defined in the vicinity of and at said notch to limit the number of possible oscillation frequencies at the notch to a finite number, and
- means for automatically controlling the location of said at least one notch in the response of said moving-average filter means in accordance with the output from said moving-average filter,
- wherein said moving-average filter means comprises:
- clock means for generating a clock signal;
- and
- memory means for sampling the output from said amplification means in accordance with said clock signal and for storing and shifting M+1 samples also in accordance with said clock signal, and
- wherein said controlling means comprises automatic clock control means for controlling the frequency of said clock signal in accordance with the output from said moving-average filter means to thereby control the location of said at least one notch in the frequency response of said moving-average filter means.
9 more elements
A sound amplification system for a hearing aid comprising:
- a microphone;
- an amplifier for amplifying the output signals from said microphone;
- a filter having a notch therein corresponding to an oscillation frequency of said amplifier signals which is to be suppressed;
- and
- a speaker for converting the output signal from said filter into excitations detectable by a listener,
- wherein the improvement comprises said filter being a moving-average filter having a frequency response with at least one notch therein, the phase characteristic of the transfer function for said moving-average filter being well-defined in the vicinity of and at said notch to limit the number of possible oscillation frequencies at the notch to a finite number, and
- means for automatically controlling the location of said at least one notch in the response of said moving-average filter in accordance with the output from said moving-average filter,
- wherein said moving-average filter comprises:
- clock means for generating a clock signal;
- and
- memory means for sampling the output from said amplifier in accordance with said clock signal and for storing at least M+1 samples, and
- wherein said controlling means comprises automatic clock control means for controlling the frequency of said clock signal in accordance with the output from said moving-average filter to thereby control the location of said at least one notch in the frequency response of said moving-average filter.
9 more elements
Dependencies are inferred from the claim text.