Adaptive noise control system with secondary path estimation

An active noise cancellation system for reducing, at a listening position, power of a noise signal radiated from a noise source to the listening position, the system comprising:

• an adaptive filter that receives a reference signal representing the noise signal, and provides a compensation signal in response to the received reference signal;
• a signal source that provides a measurement signal;
• an acoustic actuator that radiates the compensation signal and the measurement signal to the listening position;
• a microphone that receives a first signal that is a superposition of the radiated compensation signal, the radiated measurement signal, and the noise signal at the listening position, and provides a microphone signal in response to the received first signal;
• a secondary path comprising a secondary path system that represents a signal transmission path between an output of the adaptive filter and an output of the microphone;
• an estimation device that estimates a transfer characteristic of the secondary path system in response to the measurement signal and the microphone signal;
• and
• a pre-processing device connected upstream of the at least one acoustic actuator and downstream of the adaptive filter, the pre-processing device comprising a device for imposing a frequency dependent gain on the measurement signal.

A method for reducing, at a listening position, power of a noise signal radiated from a noise source to the listening position, the method comprising:

• adaptively filtering a reference signal representing the noise signal via an adaptive filter to provide a compensation signal at a first sample rate;
• providing a measurement signal;
• an acoustic actuator;
• receiving a first signal via at least one microphone, where the first signal is a superposition of the radiated compensation signal, the radiated measurement signal, and the noise signal at the listening position;
• and
• estimating a transfer characteristic of a secondary path system responsive to the measurement signal and the first signal;
• where the secondary path system represents a signal transmission path between an output of the adaptive filter and an output of the at least one microphone;
• adjusting the first sampling rate to match a second sample rate of an audio system driving the acoustic actuator;
• all-pass filtering the measurement signal to provide substantially the same signal phase shift in both signal paths, the signal path providing the measurement signal and the compensation signal;
• and
• superposing the measurement signal and the compensation signal and providing a sum signal indicative thereof to the acoustic actuator.

An active noise cancellation system for reducing, at a listening position, power of a noise signal radiated from a noise source to the listening position, the system comprising:

• an adaptive filter that receives a reference signal representing the noise signal, and provides a compensation signal at a first sample rate;
• a signal source that provides a measurement signal;
• an acoustic actuator that radiates the compensation signal and the measurement signal to the listening position;
• a microphone that receives a first signal that is a superposition of the radiated compensation signal, the radiated measurement signal, and the noise signal at the listening position, and provides a microphone signal;
• a secondary path comprising a secondary path system that represents a signal transmission path between an output of the adaptive filter and an output of the microphone;
• an estimation device that estimates a transfer characteristic of the secondary path system in response to the measurement signal and the microphone signal;
• and
• a pre-processing device configured to superpose the measurement signal and the compensation signal and provide resulting sum signals to the acoustic actuator, where the pre-processing device comprises a sample rate converter that adjusts the first sampling rate to substantially match a second sampling rate of an audio system driving the acoustic actuator, where the pre-processing device comprises an all-pass filter that provides substantially the same phase shift in a first signal path that provides the measurement signal and in a second signal path that provides the compensation signal.