Method for tuning an adaptive leaky LMS filter

• US 6,741,707 B2
• Filed: 06/22/2001
• Issued: 05/25/2004
• Est. Priority Date: 06/22/2001
• Status: Active Grant

• Current Assignee: The Trustees of Dartmounth College (Dartmouth College)
• Original Assignee: The Trustees of Dartmounth College (Dartmouth College)
• Inventors: Ray, Laura R., Collier, Robert Douglas, Cartes, David A.
• Primary Examiner(s): Harvey, Minsun Oh
• Application Number:
  US09/887,942
• Publication Number:
  US 20030026438A1
• Time in Patent Office: 1,068 Days
• Field of Search: 381/71.6, 381/71.1, 381/71.7, 381/71.11, 381/71.12, 381/94.1, 381/74
• US Class Current: 381/71.11
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17855 for improving speed or power requirements
• CPC Class Codes: G10K 11/17861 using additional means for damping sound, e.g. using sound absorbing panels
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone

Abstract

A method to automatically and adaptively tune a leaky, normalized least-mean-square (LNLMS) algorithm so as to maximize the stability and noise reduction performance in feedforward adaptive noise cancellation systems. The automatic tuning method provides for time-varying tuning parameters λ_k and μ_k that are functions of the instantaneous measured acoustic noise signal, weight vector length, and measurement noise variance. The method addresses situations in which signal-to-noise ratio varies substantially due to nonstationary noise fields, affecting stability, convergence, and steady-state noise cancellation performance of LMS algorithms. The method has been embodied in the particular context of active noise cancellation in communication headsets. However, the method is generic, in that it is applicable to a wide range of systems subject to nonstationary, i.e., time-varying, noise fields, including sonar, radar, echo cancellation, and telephony.

Claims

1. A method of tuning an adaptive feedforward noise cancellation algorithm, comprising the acts of:

providing a feedforward LMS tuning algorithm including at least first and second time varying parameters wherein said feedforward LMS tuning algorithm includes the formulas;

2. A method of tuning an algorithm for providing noise cancellation, comprising the acts of:

receiving a measured reference signal, the measured reference signal including a measurement noise component having a measurement noise value of known variance; and

generating an acoustic noise cancellation signal according to the formulas;

3. A method of tuning a least mean square (LMS) filter comprising the acts of:

formulating a Lyapunov function of a LMS filter weight vector, a reference input signal, a measurement noise on the measured reference input signal, a time varying leakage parameter λ

_k, and a step size parameter μ

_k;

using the resultant Lyapunov function to identify formulas for computing the time varying leakage parameter λ

_k and step size parameter μ

_k that maximize stability and performance of the resultant LMS filter weight vector update equation

4. A method of tuning a filter of the least mean square (LMS) type for providing noise cancellation comprising the acts of:

receiving a measured reference signal X_k=X_k+Q_k of an acoustic noise X_k to be cancelled, a measured reference signal X_k being comprised of a past L samples of the acoustic noise signal and including a measurement noise component Q_k having a known or measured variance;

receiving a measured error signal e_k resulting from application of the noise cancellation signal to the acoustic noise;

generating an acoustic noise cancellation signal y_k according to the formulas;

5. The method of tuning as claimed in claim 4 wherein the reference signal is acquired using a microphone, a microphone preamplifier and a signal conditioner, and is sampled using an analog-to-digital converter.

6. The method of tuning as claimed in claim 4 wherein the error signal is acquired using a microphone, a microphone preamplifier and a signal conditioner, and is sampled using an analog-to-digital converter.

7. The method of tuning as claimed in claim 4 wherein the acoustic noise signal is output through a digital-to-analog converter, a signal conditioner, and an audio amplifier to a speaker to generate the noise cancellation signal.

8. The method of tuning as claimed in claim 4 wherein said method provides noise control in a hearing protection device, wherein said measured reference signal is acquired using a microphone mounted on an external surface of the hearing protection device, said error signal is acquired using a microphone mounted on an inside surface of the hearing protection device to measure a sound pressure level in a space between an ear canal and an internal surface of the hearing protection device, and a noise cancellation speaker is mounted on the inside surface of the hearing protection device to produce a noise cancellation signal in the space between the ear canal and the internal surface of the hearing protection device.