Perceptual weighting device and method for efficient coding of wideband signals

Abstract

A perceptual weighting device for producing a perceptually weighted signal in response to a wideband signal comprises a signal pre-emphasis filter, a synthesis filter calculator, and a perceptual weighting filter. The signal pre-emphasis filter enhances the high frequency content of the wideband signal to thereby produce a pre-emphasized signal. The signal pre-emphasis filter has a transfer function of the form: P(z)=1−μz−1, wherein μ is a pre-emphasis factor having a value located between 0 and 1. The synthesis filter calculator is responsive to the pre-emphasized signal for producing synthesis filter coefficients. Finally, the perceptual weighting filter processes the pre-emphasized signal in relation to the synthesis filter coefficients to produce the perceptually weighted signal. The perceptual weighting filter has a transfer function, with fixed denominator, of the form: W(z)=A(z / γ1) / (1−γ2z−1) where 0<γ2<γ1≦1.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a perceptual weighting device and method for producing a perceptually weighted signal in response to a wideband signal (0-7000 Hz) in order to reduce a difference between a weighted wideband signal and a subsequently synthesized weighted wideband signal. [0003] 2. Brief Description of the Prior Art [0004] The demand for efficient digital wideband speech / audio encoding techniques with a good subjective quality / bit rate trade-off is increasing for numerous applications such as audio / video teleconferencing, multimedia, and wireless applications, as well as Internet and packet network applications. Until recently, telephone bandwidths filtered in the range 200-3400 Hz were mainly used in speech coding applications. However, there is an increasing demand for wideband speech applications in order to increase the intelligibility and naturalness of the speech signals. A bandwidth in the rang...

AI Technical Summary

Benefits of technology

[0014] More specifically, in accordance with the present invention, there is provided a perceptual weighting device for producing a perceptually weighted signal in response to a wideband signal in order to reduce a difference between a weighted wideband signal and a subsequently synthesized weighted wideband signal. This perceptual weighting device comprises:

[0015] a) a signal preemphasis filter responsive to the wideband signal for enhancing the high frequency content of the wideband signal to thereby produce a preemphasised signal;

[0025] The solution to the problem exposed in the brief description of the prior art is accordingly to introduce a preemphasis filter at the input, compute the synthesis filter coefficients based on the preemphasized signal, and use a modified perceptual weighting filter by fixing its denominator. By reducing the dynamic range of the wideband signal, the preemphasis filter renders the wideband signal more suitable for fixed-point implementation, and improves the encoding of the high frequency contents of the spectrum.

Problems solved by technology

Some difficulties arise when applying the telephone-band optimized CELP model to wideband signals, and additional features need to be added to the model in order to obtain high quality wideband signals.

Wideband signals exhibit a much wider dynamic range compared to telephone-band signals, which results in precision problems when a fixed-point implementation of the algorithm is required (which is essential in wireless applications).

Furthermore, the CELP model will often spend most of its encoding bits on the low-frequency region, which usually has higher energy contents, resulting in a low-pass output signal.

However, it was found that this filter is not suitable for efficient perceptual weighting when it was applied to wideband signals.

It was found that this filter has inherent limitations in modelling the formant structure and the required spectral tilt concurrently.

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