Method for signalling a noise substitution during audio signal coding

A method for coding an audio signal, comprising the following steps:

• signalling a noise substitution by means of the following substeps:
• transforming a time-domain audio signal into the frequency domain to obtain spectral values;
• grouping the spectral values together to form groups of spectral values, each group having assigned side information, the side information having a defined code book number place for receiving a code book number;
• detecting whether a group of spectral values is a noisy group;
• if a group is not noisy, allocating a code book from a plurality of code books for a redundancy coding of the non-noisy group, the code book allocated to the group being referred to by means of a code book number, the code book number being inserted in the defined code book number place of the side information for the non-noisy group;
• and
• if a group is noisy, allocating an additional code book number, which does not refer to a code book, to the noisy group to signal that this group is noisy and is therefore not redundancy coded, the additional code book number to be inserted in the defined code book number place of the side information for the noisy group;
• calculating a measure of the energy of the noisy group;
• entering the measure of the energy in the side information assigned to the noisy group;
• entering the additional code book number in the defined code book number place of the side information assigned to the noisy group;
• quantizing the non-noisy groups and redundancy coding the quantized non-noisy groups using the code book referred to by the code book number, whereas no quantization or coding takes place for noisy groups;
• and
• forming a bit stream which comprises as main information quantized and redundancy coded non-noisy groups and as side information, for noisy groups, the measure of the energy of the spectral values of the noisy groups and the additional code book number for signalling the noisy groups.

A method for decoding a coded audio signal, comprising the following steps:

• receiving a bit stream including side information, the side information having a defined code book number place;
• redundancy decoding non-noisy groups on the basis of a code book indicated by a code book number at the code book number place of the side information for the non-noisy groups and requantizing redundancy-decoded, quantized spectral values;
• identifying a noisy group of spectral values on the basis of an additional code book number at the code book number place of the side information for the non-noisy group-which is assigned to the non-noisy group;
• establishing a measure of the energy of the spectral values in the noisy group on the basis of the side information assigned to the group;
• generating noise spectral values for the noisy group, the measure of the energy of the noise spectral values in the noisy group being the same as the measure of the energy of the spectral values of the noisy group in an audio signal before coding;
• and
• converting the requantized spectral values and the noise spectral values into a time domain representation to obtain a decoded audio signal.