Subband adaptive filter for systems with partially acausal transfer functions

A noise reduction system comprising:

• one or more feedforward sensors configured to generate an input signal;
• one or more feedback sensors configured to generate a feedback signal;
• an adaptive system identification filter configured to represent a transfer function of a path traversed by the input signal;
• one or more processing devices, configured to
• receive the input signal and the feedback signal;
• generate, based on the input signal and the feedback signal, an updated set of filter coefficients of the adaptive system identification filter, wherein generating the updated set of filter coefficients of the adaptive system identification filter comprises:
• (i) separating the input signal into multiple frequency subbands,
• (ii) separating the feedback signal into the multiple frequency subbands,
• (iii) determining, for each frequency subband, one or more coefficients of a corresponding subband adaptive module, and
• (iv) combining one or more coefficients of multiple subband adaptive modules to generate the updated set of filter coefficients of the adaptive system identification filter,
• wherein determining the one or more coefficients of the corresponding subband adaptive module comprises:
• (a) obtaining a precomputed set of filter coefficients of the adaptive system identification filter, and
• (b) selecting a subset of the precomputed set of filter coefficients of the adaptive system identification filter, a number of coefficients in the subset being less than a number of the precomputed set of filter coefficients of the adaptive system identification filter;
• and
• process a portion of the input signal using the updated set of filter coefficients of the adaptive system identification filter to generate an output that destructively interferes with another signal traversing the path represented by the transfer function;
• and
• one or more transducers, driven by the output generated by the one or more processing devices.

One or more non-transitory computer readable media storing instructions that are executable by one or more processing devices, and upon such execution cause the one or more processing devices to perform operations comprising:

• receiving an input signal;
• receiving a feedback signal;
• generating, based on the input signal and the feedback signal, an updated set of filter coefficients of an adaptive system identification filter configured to represent a transfer function of a path traversed by the input signal, wherein generating the updated set of filter coefficients of the adaptive system identification filter comprises:
• (i) separating the input signal into multiple frequency subbands,
• (ii) separating the feedback signal into the multiple frequency subbands,
• (iii) determining, for each frequency subband, one or more coefficients of a corresponding subband adaptive module, and
• (iv) combining one or more coefficients of multiple subband adaptive modules to generate the updated set of filter coefficients of the adaptive system identification filter,
• wherein determining the one or more coefficients of the corresponding subband adaptive module comprises:
• (a) obtaining a precomputed set of filter coefficients of the adaptive system identification filter, and
• (b) selecting a subset of the precomputed set of filter coefficients of the adaptive system identification filter, a number of coefficients in the subset being less than a number of the precomputed set of filter coefficients of the adaptive system identification filter;
• and
• processing a portion of the input signal using the updated set of filter coefficients of the adaptive system identification filter to generate an output that destructively interferes with another signal traversing the path represented by the transfer function.