Abstract: Audio sources are coded by recognizing different classes of audio such as speech and music. The classes are used to select between coding algorithms and to provide object definitions. Objects have abstract and concrete classes which may further rely on parameters produced by linear prediction and subband filters to provide a frame-based bit stream of information. Each object in the bit stream has layers of information such as basic bit rate, coding parameters and enhancement parameters. The layers of information in each object allow altering selected parameters to manipulate audio signals.

Abstract: A method and a device for speech signal digital coding are provided where at each frame there is carried out a long-term analysis for estimating pitch period d and a long- term prediction coefficient b and gain G, and an a-priori classification of the signal as active/inactive and, for active signal, as voiced/unvoiced. Period estimation circuits (LT1) compute such period on the basis of a suitably weighted covariance function, and classification circuits (RV) distinguish voiced signals from unvoiced signals by comparing long-term prediction coefficient and gain with frame-by-frame variable thresholds.

Abstract: An optimum excitation signal for each subframe is determined in a speech coder based on analysis-by-synthesis techniques and operating on frames of samples divided into a number of subframes. The excitation signal includes a shape contribution (innovation) and an amplitude contribution (gain) which are quantized separately. A circuit (IT) for gain quantization includes means (QU) for determining a gain index for each subframe; a comparison logic network (CFR) for detecting the maximum value taken by the gain index in the frame; and means for computing a normalized index for each subframe as a difference between the maximum index and the gain index relevant to that subframe. The coded signal includes the coded values of the maximum index and of the normalized indexes as information on the gain relevant to a frame.