Digital feed-forward active noise control system

A method of noise control of an acoustic signal comprising:

• (a) obtaining a reference signal of the acoustic signal to be controlled,
• (b) applying an antinoise signal to the acoustic signal so as to control the acoustic signal,
• (c) obtaining an error signal resulting from the application of the antinoise signal to the acoustic signal,
• (d) generating said antinoise signal from said reference signal by passing the reference signal through a first filter having controllable filter coefficients,
• (e) controlling the filter coefficients by processing the error signal and a modified representation of the reference signal and generating a coefficient control signal such as to generate the antinoise signal,
• (f) applying the coefficient control signal to the first filter, and
• (g) oversampling the reference and error signals at a sampling frequency of 40 kHz, or lower, and controlling said first filter coefficients by processing only a time-spaced fraction of the oversampled samples of the reference and error signals, said fraction being about one quarter or less, and applying said antinoise signal to the acoustic signal at said sampling frequency.

A method of noise control of an acoustic signal comprising:

• (a) obtaining a reference signal of the acoustic signal to be controlled,
• (b) applying an antinoise signal to the acoustic signal so as to control the acoustic signal,
• (c) obtaining an error signal resulting from the application of the antinoise signal to the acoustic signal,
• (d) generating said antinoise signal from said reference signal by passing the reference signal through a first filter having controllable filter coefficients,
• (e) controlling the filter coefficients by processing the error signal and a modified representation of the reference signal and generating a coefficient control signal such as to generate the antinoise signal,
• (f) applying the coefficient control signal to the first filter, and
• (g) varying the gains of the paths of the reference signal (X), the antinoise signal (U), and the error signal (E) such that the error path impulse response remains unchanged.