Patent ID: 6134518
Filing Date: 2000-10-17
Classification: G10L

Abstract:
Apparatus for digitally encoding an input audio signal for storage or transmission wherein the input audio signal comprises a series of signal samples ordered in time and divided into frames, comprising:logic for measuring a distinguishing parameter from the input signal,determining means for determining from the measured distinguishing parameter whether the input signal contains an audio signal of a first type or a second type;first and second coders for digitally encoding the input signal using first and second coding methods respectively;a switching arrangement for, at any particular time, directing the generation of an output signal by encoding the input signal using either the first or second coders according to whether the input signal contains an audio signal of the first type or the second type at that time; andwherein the first coder is a Codebook Excited Linear Predictive (CELP) coder and the second coder is a transform coder, each coder being arranged to operate on a frame-by-frame basis, the transform coder being arranged to encode a frame using a discrete frequency domain transform of a range of samples from a plurality of neighboring frames, and wherein the CELP coder is arranged to encode an extended frame to generate the last CELP encoded data prior to a switch from a mode of operation in which frames are encoded using the transform coder, the extended frame covers the same range of sample as the transform coder, so that a transform decoder can generate the information required to decode the first frame encoded using the transform coder from the last CELP encoded frame.