DSP control algorithms for canceling broadband random noise with a single microphone and speaker.
Thomas R. Harley, James E. Hendrix, F. Douglass Shields · The Journal of the Acoustical Society of America · 1991
Innovative and conventional techniques for making a general purpose controller are described and compared. Here, the controller is a digital signal processor which receives input representing some undesired disturbance and outputs a driving voltage to a transducer in order to counteract the disturbance. The controller is intended to optimally reduce stationary random broadband noise for which no upstream or precursor signal is available. Three different methods are presented for defining a linear IIR filter which is implemented by the controller. For one of these methods, the digital filter yielding the minimum power is calculated numerically by integrating the theoretically predicted power spectrum over frequency space. This power spectrum can be easily modified by an arbitrary frequency dependent weighting factor, such as the sensitivity of the human ear. Experimental results are given. Theoretical analysis of the performance to be expected from a conventional LMS algorithm used in single microphone and speaker systems is given for a specific application which reveals inherent problems associated with the conventional approach.