Anc convergence factor estimation as a function of frequency

A method of operating an audio system in a vehicle, the method comprising:

• providing a plurality of microphones associated with a passenger compartment of the vehicle, the microphones being configured to produce a plurality of microphone signals;
• providing a plurality of loudspeakers associated with the passenger compartment of the vehicle;
• estimating a plurality of convergence factors for use in performing active noise control, the estimating including:
• calculating an Eigen value of an autocorrelation matrix of a passenger compartment transfer function, the Eigen value being a function of a rotational speed of an engine of the vehicle;
• determining an engine rotational speed associated with a local minimum of the Eigen value;
• finding by experimentation a largest stable value for one of the convergence factors at a minimum engine speed;
• calculating a calibration factor dependent upon the largest stable value for one of the convergence factors at a minimum engine speed;
• and
• estimating all values of the convergence factor within a range of engine speeds, the estimating being dependent upon the calibration factor and the Eigen values within the range of engine speeds;
• and
• transmitting a plurality of active noise controlled audio signals to the loudspeaker, the active noise controlled audio signals being dependent upon the microphone signals and the estimated convergence factor values.

A method of operating an audio system in a vehicle, the method comprising:

• providing at least one microphone associated with a passenger compartment of the vehicle, the microphone being configured to produce a plurality of microphone signals;
• providing at least one loudspeaker associated with the passenger compartment of the vehicle;
• estimating a plurality of convergence factors for use in performing active noise control, the estimating including:
• calculating an Eigen value of an autocorrelation matrix of a passenger compartment transfer function;
• calculating a calibration factor dependent upon a largest stable value for one of the convergence factors at a minimum engine speed;
• and
• estimating all values of the one convergence factor within a range of engine speeds, the estimating being dependent upon the calibration factor and a plurality of Eigen values within the range of engine speeds;
• and
• transmitting a plurality of active noise controlled audio signals to the loudspeaker, the active noise controlled audio signals being dependent upon the microphone signals and the estimated convergence factor values.