Gerhard Schmidt

Step-size control for acoustic echo cancellation filter—an overview

Abstract In this paper we present an overview about several approaches for controlling the step size for adaptive echo cancellation filters in hands-free telephones. First an optimal step size is derived. For the determination of this step size the power of a non-measurable signal has to be estimated. Detection and estimation methods for the determination of this power and for the determination of the optimal step size can be grouped into four classes. For each class, several principles, which differ in their reliability and in their complexity, are presented. Possibilities for combining elements from each class to create an entire step size control unit are also described. An outlook on detector combinations based on neuronal networks concludes this paper.

Hands-free telephones: joint control of echo cancellation and postfiltering

Abstract This paper deals with an efficient and robust joint control of the step sizes of subband adaptive echo compensation filters and the frequency response of the echo suppression filter of a hands-free telephone system. It is shown that both control methods are described by the same quantity: the ratio of the short-term estimates of the power of the error to the “undisturbed” error signal. Since the latter is not directly measurable, a three-step procedure for its estimation is given. It uses speech activity detection, a “shadow” filter, and a correlation analysis. The procedure described has been implemented. It produced a considerable reduction in the amount of necessary signal processing. Furthermore, it was possible to provide natural communication with hands-free telephone systems.

Chapter 8. Acoustic Array Processing for Speech Enhancement

This chapter contains sections titled: Introduction Signal Processing in Subband Domain Multichannel Echo Cancellation Speaker Localization Beamforming Sensor Calibration Postprocessing Conclusions References

Algorithms for Adaptive Filters

This chapter includes the following topics: The Normalized Least Mean Square Algorithm The Affine Projection Algorithm The Recursive Least Squares Algorithm The Kalman Algorithm ]]>

Control of Noise and Echo Suppression Systems

This chapter includes the following topics: Estimation of Spectral Power Density of Background Noise Musical Noise Control of Filter Characteristics

Traditional Methods for Stabilization of Electroacoustic Loops

This chapter includes the following topics: Adaptive Line Enhancement Frequency Shift Controlled Attenuation