Audio encoder, audio decoder, method for encoding and decoding an audio information, and computer program obtaining a context sub-region value on the basis of a norm of previously decoded spectral values

摘要

An audio decoder for providing a decoded audio information on the basis of an encoded audio information comprises an arithmetic decoder for providing a plurality of decoded spectral values on the basis of an arithmetically-encoded representation of the spectral values and a frequency-domain-to-time-domain converter for providing a time-domain audio representation using the decoded spectral values, in order to obtain the decoded audio information. The arithmetic decoder is configured to select a mapping rule describing a mapping of a code value onto a symbol code in dependence on a context state described by a numeric current context value. The arithmetic decoder is configured to determine the numeric current context value in dependence on a plurality of previously decoded spectral values. The arithmetic decoder is configured to obtain a plurality of context subregion values on the basis of previously decoded spectral values and to store said context subregion values. The arithmetic decoder is configured to derive a numeric current context value associated with one or more spectral values to be decoded in dependence on the stored context subregion values. The arithmetic decoder is configured to compute the norm of a vector formed by a plurality of previously decoded spectral values in order to obtain a common context subregion value associated with the plurality of previously decoded spectral values. An audio encoder uses a similar concept.