Adaptive digital noise canceller

Abstract

Systems and methods for adaptive feed-forward noise cancellation. The system includes a plurality of reference microphones, an error microphone, a secondary path module, an adaptation controller, and a canceller filter. A finite impulse response ("FIR") based plant model is converted to an infinite impulse response ("HR") based plant model using balanced model reduction. Due to the inherent instability of the adaptive HR filter, the Schur-Cohn stability test is applied to the denominator coefficients of the HR filter transfer function to determine the stability of the noise cancellation system. A secondary path of the noise cancellation system is identified in an on-line manner in the secondary path module. If the energy level of the communication signal (e.g., a music signal) is strong, secondary path identification is performed.; The adaptation controller controls the updating of the HR transfer function based on the stability determination and the secondary path. An anti-noise signal is then generated and added to the communication signal. The anti-noise signal is generated within approximately 60 or fewer micro-seconds.

Description

technical field [0001] The present invention relates to noise canceling headphones (eg, headphones, earbuds, etc.). Background technique [0002] Noise-cancelling headphones are used in high-noise environments, such as airplane cockpits or near loud machinery, and elsewhere. Various techniques have been developed to provide noise cancellation in headphones. For example, many conventional noise cancellers use analog noise cancellation and use feedback or feedforward control techniques. Feedback noise cancellation is often used in headphones with loud chambers. Feed-forward noise cancellation is commonly used in earbuds and on-ear headphones. [0003] Feedforward noise cancellers use the principle of superposition to cancel unwanted ambient noise signals reaching the wearer's ears. For example, a feed-forward noise canceller uses a canceller filter based on a plant model (eg, transfer function) of the earphone to generate an anti-noise signal. Specifically, the canceller ...

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However, there are also secondary paths that affect noise cancellation

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