Method and apparatus for encoding and decoding excitation patterns from which the masking levels for an audio signal encoding and decoding are determined

Method for encoding excitation patterns from which the masking levels for an audio signal encoding are determined following a corresponding excitation pattern decoding, wherein for said audio signal encoding said audio signal is processed successively using different window and spectral transform lengths and a section of the audio signal representing a given multiple of the longest transform length is denoted a frame, and wherein said excitation patterns are related to a spectral representation of successive sections of said audio signal, said method including the steps:

• a) forming, for a current frame of said audio signal, in each case for a corresponding group of successive excitation patterns an excitation pattern matrix P, wherein for each one of said different spectral transform lengths a corresponding excitation pattern is included in said matrix P, and taking the logarithm of each matrix P entry,
• and wherein, in case the resulting matrix size is not suited for the transform of the following step, the size of the matrix is increased by copying a necessary number of times the values of an excitation pattern located at the matrix border;
• b) applying a two-dimensional transform on the logarithmized matrix P values, resulting in matrix PT;
• c) applying a pre-determined sorting order to the coefficients in said matrix PT, said pre-determined sorting order depending on the matrix size, which matrix size depends on the number of non-longest transform lengths in the current frame and is represented by a corresponding sorting index,
• and, taking only a fixed number of values of the corresponding sorting path starting from the first value, forming a quadratic version PTq of matrix PT with these values;
• d) carrying out a SPECK encoding for matrix PTq, in which SPECK encoding bit planes of the matrix PTq are processed and a successive partitioning is used for locating and coding the positions of the corresponding coefficient bits in said bit planes.

Audio signal encoder in which excitation patterns are encoded from which the masking levels for an encoding of said audio signal are determined following a corresponding excitation pattern decoding, wherein for encoding said audio signal it is processed successively using different window and spectral transform lengths and a section of the audio signal representing a given multiple of the longest transform length is denoted a frame, and wherein said excitation patterns are related to a spectral representation of successive sections of said audio signal, said apparatus including:

• means being adapted for forming, for a current frame of said audio signal, in each case for a corresponding group of successive excitation patterns an excitation pattern matrix P, wherein for each one of said different spectral transform lengths a corresponding excitation pattern is included in said matrix P, and for taking the logarithm of each matrix P entry,
• and wherein, in case the resulting matrix size is not suited for the transform of the following step, the size of the matrix is increased by copying a necessary number of times the values of an excitation pattern located at the matrix border,
• and wherein a two-dimensional transform is applied on the logarithmized matrix P values, resulting in matrix PT,
• and wherein a pre-determined sorting order is applied to the coefficients in said matrix PT, said pre-determined sorting order depending on the matrix size, which matrix size depends on the number of non-longest transform lengths in the current frame and is represented by a corresponding sorting index,
• and wherein, taking only a fixed number of values of the corresponding sorting path starting from the first value, a quadratic version PTq of matrix PT is formed with these values;
• means being adapted for carrying out a SPECK encoding for matrix PTq, in which SPECK encoding bit planes of the matrix PTq are processed and a successive partitioning is used for locating and coding the positions of the corresponding coefficient bits in said bit planes.