System for computationally efficient active control of tonal sound or vibration

A method for computing control commands at a reduced rate in a noise or vibration control system including the steps of:

• a) sensing a physical variable;
• b) identifying harmonic components (ak, bk) of the physical variable at a frequency of interest (fd);
• c) down-sampling the harmonic components (ak, bk) to a lower update frequency (fu);
• d) performing control computations on the harmonic components (ak, bk) at the lower update frequency (fu);
• and
• e) generating control commands based upon the control computations.

A method for analyzing a physical variable having a first frequency of interest f1 and a second frequency of interest f2 including the steps of:

• a) identifying first harmonic components ak1, bk1 of the first frequency of interest f1;
• b) down-sampling the harmonic components ak1, bk1 at an intermediate frequency fu1;
• c) identifying second harmonic components ak2, bk2 of a difference between the first frequency of interest f1 and the second frequency of interest f2;
• d) downsampling the harmonic components ak2, bk2 at an update frequency fu2;
• and
• e) analyzing information at the first frequency of interest f1 and the second frequency of interest f2 based upon said harmonic components ak1, bk1 and ak2, bk2.

An apparatus for sensing physical variables at a reduced rate comprising:

• a sensor adapted to sense physical variables and to generate a sensed signal as a function of the sensed physical variable;
• and
• a control circuit adapted to establish a frequency of interest (fd), and to establish a sample frequency (fs),
• wherein the control circuit filters the sensed signals to extract a frequency range with a lower bound given by (2n−1)*fs/2 and an upper bound given by (2n+1)*fs/2, where n is an integer chosen so that the frequency of interest (fd) is within the extracted frequency range.