Speech decoder and method for decoding speech

Abstract

A speech decoder comprises a decoder (103) for converting a linear prediction encoded speech signal into a first sample stream having a first sampling rate and representing a first frequency band. Additionally it comprises a vocoder (105) for converting an input signal into a second sample stream having a second sampling rate and representing a second frequency band, and combination means (107) for combining the first and second sample streams in processed form. It comprises also means (301) for generating a second linear prediction filter, to be used by the vocoder (105) on the second frequency band, on the basis of a first linear prediction filter used by the decoder (103) on the first frequency band. Extrapolation through an infinite impulse response filter is the preferable method of generating the second linear prediction filter.

Description

technical field [0001] The present invention generally relates to techniques for decoding digitally encoded speech. In particular, the present invention relates to techniques for generating wideband decoded output signals from narrowband encoded input signals. Background technique [0002] Digital telephone systems have traditionally relied on standardized speech encoding and decoding procedures with fixed sampling rates to ensure compatibility between arbitrarily chosen transmitter-receiver pairs. The development of second-generation digital cellular networks and their enhanced terminals has led to a situation where complete one-to-one compatibility with respect to sampling rates cannot be guaranteed, that is, speech coders in transmitting terminals can use An input sampling rate different from the output sampling rate of the speech decoder in the terminal. Due to complexity constraints, a linear prediction or LP (linear prediction) analysis of the original speech signal ...

AI Technical Summary

Problems solved by technology

The development of second-generation digital cellular networks and their enhanced terminals has led to a situation where complete one-to-one compatibility with respect to sampling rates cannot be guaranteed, that is, speech coders in transmitting terminals can use An input sample rate different from the output sample rate of the speech decoder in the terminal

[0009] The use of look-up tables in the search for appropriate wideband filter characteristics can help avoid disasters of the kind shown in Figure 2, but at the same time introduce considerable inflexibility

Either only a limited number of possible broadband filters can be implemented, or very large memories have to be allocated just for this purpose

Increasing the number of stored wideband filters from which to choose also increases the time that must be allotted for searching and establishing the correct configuration among them, which is undesirable in real-time operations such as voice telephony

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