Audio directivity coding

An apparatus for decoding audio metadata, wherein an encoded representation of the audio metadata is received from a bitstream, the audio metadata being according to different directions, the directions being associated with discrete positions on a unit sphere, the discrete positions on the unit sphere being displaced according to parallel lines from an equatorial line towards a first pole and from the equatorial line towards a second pole, the apparatus comprising:

• a bitstream reader configured to acquire prediction residual values from the encoded representation of the audio metadata received from the bitstream;
• a prediction section configured to acquire the audio metadata by prediction and from prediction residual values of the audio metadata, the prediction section using a plurality of prediction sequences comprising:
• at least one initial prediction sequence, along a line of adjacent discrete positions, predicting the audio metadata based on the immediately preceding audio metadata in the same initial prediction sequence;
• and
• at least one subsequent prediction sequence, divided among a plurality of subsequences, each subsequence moving along a parallel line and being adjacent to a previously predicted parallel line, and being such that audio metadata along a parallel line being processed are predicted based on at least:
• audio metadata of the adjacent discrete positions in the same subsequence;
• and
• interpolated versions of the audio metadata of the previously predicted adjacent parallel line, each interpolated version of the adjacent previously predicted parallel line comprising the same number of discrete positions of the parallel line being processed;
• wherein the apparatus is configured to acquire, using the audio metadata acquired by the prediction section, a decoded audio metadata signal and to render the decoded audio metadata signal.

An audio decoding method for decoding audio values, the audio values being according to different directions, the directions being associated with discrete positions on a unit sphere, the discrete positions on the unit sphere being displaced according to parallel lines from an equatorial line towards a first pole and from the equatorial line towards a second pole, the method comprising:

• receiving an encoded representation of the audio values from a bitstream;
• acquiring prediction residual values from the encoded representation of the audio values received from the bitstream;
• decoding the prediction residual values and predicted values from a plurality of prediction sequences comprising:
• at least one initial prediction sequence, along a line of adjacent discrete positions, predicting audio values based on the audio values of the immediately preceding audio values in the same initial prediction sequence;
• and
• at least one subsequent prediction sequence, divided among a plurality of subsequences, each subsequence moving along a parallel line and being adjacent to a previously predicted parallel line, and being such that audio values along a parallel line being processed are predicted based on at least:
• the audio values of the adjacent discrete positions in the same subsequence;
• and
• interpolated versions of the audio values of the adjacent previously predicted parallel line, each interpolated version of the adjacent previously predicted parallel line comprising the same number of discrete positions of the parallel line being processed,
• acquiring, using the decoded prediction residual values and the decoded predicted values, a decoded audio signal and rendering the decoded audio signal.

A non-transitory digital storage medium having a computer program stored thereon to perform the method for decoding audio values, the audio values according to different directions, the directions being associated with discrete positions on a unit sphere, the discrete positions on the unit sphere being displaced according to parallel lines from an equatorial line towards a first pole and from the equatorial line towards a second pole, the method comprising:

• receiving an encoded representation of the audio values from a bitstream;
• acquiring prediction residual values from the encoded representation of the audio values received from the bitstream;
• decoding the prediction residual values and predicted values from a plurality of prediction sequences comprising:
• at least one initial prediction sequence, along a line of adjacent discrete positions, predicting audio values based on the audio values of the immediately preceding audio values in the same initial prediction sequence;
• and
• at least one subsequent prediction sequence, divided among a plurality of subsequences, each subsequence moving along a parallel line and being adjacent to a previously predicted parallel line, and being such that audio values along a parallel line being processed are predicted based on at least:
• the audio values of the adjacent discrete positions in the same subsequence;
• and
• interpolated versions of the audio values of the adjacent previously predicted parallel line, each interpolated version of the adjacent previously predicted parallel line having the same number of discrete positions of the parallel line being processed;
• acquiring, using the decoded prediction residual values and the decoded predicted values, a decoded audio signal and rendering the decoded audio signal, when said computer program is run by a computer.