Audio controller for a semi-adaptive active noise reduction device
An audio controller for an active noise reduction, ANR, reduces an ambient noise signal. The audio controller includes processing circuitry configured to provide a fixed ANR filter configured to generate a first noise reduction signal. Moreover, the processing circuitry is further configured to provide an adaptive ANR filter. The adaptive ANR filter includes one or more adjustable filter coefficients for adapting the adaptive ANR filter and the adaptive ANR filter is configured to generate a second noise reduction signal. The processing circuitry is further configured to generate a total noise reduction signal as an adjustable weighted linear combination of the first noise reduction signal and the second noise reduction signal.
1 . An audio controller for an active noise reduction (ANR) device, which is adapted for reducing an ambient noise signal, the audio controller comprising a processing circuitry configured to:
provide a fixed ANR filter, the fixed ANR filter being configured to generate a first noise reduction signal;
provide an adaptive ANR filter, the adaptive ANR filter comprising one or more adjustable filter coefficients for adapting the adaptive ANR filter and the adaptive ANR filter being configured to generate a second noise reduction signal;
generate a total noise reduction signal as an adjustable weighted linear combination of the first noise reduction signal and the second noise reduction signal;
generate the total noise reduction signal as the adjustable weighted linear combination of the first noise reduction signal and the second noise reduction signal based on an adjustable weighting coefficient a; and
determine the adjustable weighting coefficient a based on the following equation:
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wherein MM(x) denotes a magnitude measure of the argument vector x, n denotes a temporal sample index, e(n) denotes a total residual noise signal and e′(n) denotes a fractional residual noise signal.
2 . The audio controller of claim 1 , wherein the processing circuitry is further configured to determine a noise reduction estimate of the reduction of the ambient noise signal caused by the second noise reduction signal, and to determine the adjustable weighted linear combination based on the noise reduction estimate.
3 . The audio controller of claim 1 , wherein the processing circuitry is further configured to generate the total noise reduction signal as the adjustable weighted linear combination of the first noise reduction signal and the second noise reduction signal based on the following equation:
y=ay fixed +(1− a ) y adap ,
wherein y fixed denotes the first noise reduction signal, y adap denotes the second noise reduction signal, and y denotes the total noise reduction signal.
4 . The audio controller of claim 1 , wherein the processing circuitry is further configured to determine the adjustable weighting coefficient a using a root mean square as the magnitude measure MM(x).
5 . The audio controller of claim 1 , wherein the processing circuitry is further configured to estimate a secondary path transfer function, wherein the secondary path transfer function describes the modification of the the total residual noise signal resulting in the fractional residual noise signal, and wherein the processing circuitry is further configured to determine the fractional residual noise signal based on the second noise reduction signal, the total residual noise signal, and the secondary path transfer function.
6 . The audio controller of claim 1 , wherein the processing circuitry is further configured to continually adjust the adjustable weighted linear combination of the first noise reduction signal and the second noise reduction signal for generating the total noise reduction signal, wherein initially the total noise reduction signal is equal to the first noise reduction signal.
7 . The audio controller of claim 1 , wherein the processing circuitry is further configured to adjust the one or more adjustable filter coefficients of the adaptive ANR filter based on a total residual noise signal.
8 . An active noise reduction (ANR) device, the ANR device comprising the audio controller according to claim 1 and a loudspeaker, wherein the loudspeaker is configured to be driven based on the total noise reduction signal generated by the audio controller.
9 . The ANR device of claim 8 , wherein the ANR device further comprises a feedforward microphone configured to detect the ambient noise signal, wherein the fixed ANR filter is configured to generate the first noise reduction signal on the basis of the ambient noise signal, and wherein the adaptive ANR filter is configured to generate the second noise reduction signal on the basis of the ambient noise signal.
10 . The ANR device of claim 8 , wherein the ANR device further comprises a feedback microphone configured to detect a total residual noise signal, wherein the fixed ANR filter is configured to generate the first noise reduction signal on the basis of the total residual noise signal and wherein the adaptive ANR filter is configured to generate the second noise reduction signal on the basis of the total residual noise signal.
11 . The ANR device of claim 8 , wherein the ANR device further comprises a feedforward microphone configured to detect the ambient noise signal and a feedback microphone configured to detect a total residual noise signal, wherein the fixed ANR filter is configured to generate the first noise reduction signal on the basis of the ambient noise signal and the total residual noise signal and wherein the adaptive ANR filter is configured to generate the second noise reduction signal on the basis of the ambient noise signal and the total residual noise signal.
12 . An active noise reduction (ANR) method for reducing an ambient noise signal, the method comprising:
generating a first noise reduction signal with a fixed ANR filter;
generating a second noise reduction signal with an adaptive ANR filter, wherein the adaptive ANR filter comprises one or more adjustable filter coefficients for adapting the adaptive ANR filter;
generating a total noise reduction signal as an adjustable weighted linear combination of the first noise reduction signal and the second noise reduction signal;
generating the total noise reduction signal as the adjustable weighted linear combination of the first noise reduction signal and the second noise reduction signal based on an adjustable weighting coefficient a; and
determining the adjustable weighting coefficient a based on the following equation:
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wherein MM(x) denotes a magnitude measure of the argument vector x, n denotes a temporal sample index, e(n) denotes a total residual noise signal and e′(n) denotes a fractional residual noise signal.
13 . A non-transitory computer-readable storage medium storing program code which is configured to cause a computer or a processor to perform the method of claim 12 , when the program code is executed by the computer or the processor.