Anc for bt headphones

Abstract

An active noise cancellation controller for performing noise attenuation in a system over a predetermined frequency rang. The controller comprises several components: a first input for a reference signal indicative of a noise level; a second input for receiving an error signal indicative of a remnant noise level; an output for providing a noise cancellation signal; a fixed feedback controller for processing the error signal; a fixed feed-forward controller for processing the reference signal; and an adaptive feed-forward controller having a digital adaptive finite impulse response filter arranged for operation on the reference signal the error signal.

1 . A method for calculating filter coefficients for use in one or more digital fixed infinite impulse response filters of an active noise cancellation controller, each digital fixed infinite impulse response filter being a filter of a predetermined order, the method comprising the steps of:
 modelling the active noise cancellation controller as a control system in a numerical computing environment, each of the one or more digital fixed infinite impulse response filters of the active noise cancellation controller being replaced with a respective adaptive finite impulse response filter;   providing a simulated noise signal to the model of the active noise cancellation controller, the simulated noise signal being representative of the environmental noise experienced by the active noise cancellation controller in use;   operating the model of the active noise cancellation controller on the simulated noise signal so as to cause the filter coefficients of the one or more adaptive finite impulse response filters to each converge on a set of first optimum filter coefficients; and   converting each set of first optimum filter coefficients into a set of filter coefficients for the respective fixed infinite impulse response filter in dependence on the predetermined order of the respective fixed infinite impulse response filter.   
     
     
         2 . A method as claimed in  claim 1 , further comprising:
 prior to converting each set of first optimum filter coefficients into a set of filter coefficients for the respective fixed infinite impulse response filter, converting each set of first optimum filter coefficients into a set of filter coefficients for an adaptive infinite impulse response filter;   replacing each of the one or more adaptive finite impulse response filters in the model of the active noise cancellation controller with a respective adaptive infinite impulse response filter;   operating the model of the active noise cancellation controller on the simulated noise signal so as to cause the filter coefficients of the one or more adaptive infinite impulse response filters to each converge on a set of second optimum filter coefficients; and   converting each set of second optimum filter coefficients into a set of filter coefficients for the respective fixed infinite impulse response filter in dependence on the predetermined order of the respective fixed infinite impulse response filter.   
     
     
         3 . A method as claimed in  claim 1 , wherein the simulated noise signal includes both broadband and periodic signals. 
     
     
         4 . A method as claimed in  claim 1 , wherein the adaptive finite impulse response filters and the adaptive infinite impulse response filters are configured to operate in accordance with one of the following adaptive algorithms: a Least Mean Squares algorithm and a Recursive Least Squares algorithm. 
     
     
         5 . An active noise cancellation controller configured substantially as described herein with reference to any of  FIGS. 10 to 17 .