Realisation of controller transfer function for active noise cancellation

Abstract

An apparatus for realizing an active noise cancellation control law transfer function between a sensing microphone and a speaker. The apparatus includes a multiplicity of filters. Each filter is operable over a different frequency range. At least one filter has an adjustable parameter whereby the filter can be adjusted such that the filters cumulatively realize a required control law transfer function. The adjustable parameter may in one embodiment be the amplitude. In other embodiments, it may be other parameters.

1 . Apparatus for realising an active noise cancellation control law transfer function between a sensing microphone and a speaker, the apparatus including a plurality of filters, each filter being operable over a different frequency range, and at least one filter having at least one adjustable parameter whereby the filter can be adjusted such that the filters cumulatively realise a required control law transfer function. 
     
     
         2 . Apparatus as claimed in  claim 1  wherein each filter includes at least one adjustable parameter. 
     
     
         3 . Apparatus as claimed in  claim 2  wherein the adjustable parameter is amplitude. 
     
     
         4 . Apparatus as claimed in  claim 2  wherein the adjustable parameter is bandwidth. 
     
     
         5 . Apparatus as claimed in  claim 1  wherein the adjustable filter comprises a parametric filter. 
     
     
         6 . Apparatus as claimed in  claim 1  wherein the adjustable parameter is dynamically adjustable. 
     
     
         7 . Apparatus as claimed in  claim 6  further comprising an adjustment controller to adjust the adjustable parameter. 
     
     
         8 . A method of active noise cancellation for apparatus including a speaker and sensing microphone and a plurality of filters, each filter being operable over a different frequency range, and at least one filter having at least one adjustable parameter whereby the filter can be adjusted, the method including:
 determining one or more acoustic or electro-acoustic characteristics of the apparatus, and;   adjusting the adjustable parameter dependent on the characteristic such that the filters cumulatively realise a control law transfer function to implement active noise cancellation.   
     
     
         9 . A method of active noise cancellation for apparatus including a speaker and sensing microphone and a plurality of filters, each filter being operable over a different frequency range, and at least one filter having at least one adjustable parameter whereby the filter can be adjusted, the method including:
 sensing the noise cancellation performance of the apparatus, and;   adjusting the adjustable parameter dependent on the sensed performance such that the filters cumulatively realise a control law transfer function to implement active noise cancellation.   
     
     
         10 . A method as claimed in  claim 9  further comprising dynamically adjusting the adjustable parameter.