Audio signal processing apparatuses and methods

An audio signal downmixing method (200), comprising:

• receiving an input audio signal including a plurality of input channels (113);
• computing (211) a plurality of eigenvectors of a covariance matrix (COV) defined by the plurality of input channels (113) of the input audio signal;
• determining (212) for at least one eigenvector of the plurality of eigenvectors of the covariance matrix (COV) a subspace angle between the at least one eigenvector and a vector defined by a column of a primary downmix matrix (DU);
• selecting (213) at least one eigenvector from the plurality of eigenvectors based on the subspace angle and a preset threshold angle θMIN;
• defining (214) at least one column of the auxiliary downmix matrix (DW) by the at least one selected eigenvector;
• and
• processing the input audio signal into an output audio signal including a plurality of primary output channels (123) and at least one auxiliary output channel (125) using a downmix matrix (D), wherein the downmix matrix (D) includes the primary downmix matrix (DU) for providing the plurality of primary output channels (123) and the auxiliary downmix matrix (DW) for providing the at least one auxiliary output channel (125).

An audio signal upmixing apparatus (139), comprising:

• a receiver configured to receive an input audio signal including a plurality of primary input channels (135) and at least one auxiliary input channel (145);
• an auxiliary upmix matrix determiner (137) configured to determine an auxiliary upmix matrix by:
• obtaining a plurality of eigenvectors of a covariance matrix (COV) of the input audio signal;
• determining for at least one eigenvector of the plurality of eigenvectors of the covariance matrix (COV) a subspace angle between the at least one eigenvector and a vector defined by a column of a primary upmix matrix;
• selecting at least one eigenvector from the plurality of eigenvectors based on the subspace angle and a preset threshold angle θMIN;
• and
• defining at least one column of the auxiliary upmix matrix by the at least one selected eigenvector;
• and
• a processor (141) configured to process the input audio signal into an output audio signal (149) using an upmix matrix, wherein the upmix matrix comprises the primary upmix matrix and the auxiliary upmix matrix.

An audio signal upmixing method, comprising:

• receiving an input audio signal including a plurality of primary input channels (135) and at least one auxiliary input channel (145);
• obtaining a plurality of eigenvectors of a covariance matrix (COV) of the input audio signal;
• determining for at least one eigenvector of the plurality of eigenvectors of the covariance matrix (COV) a subspace angle between the at least one eigenvector and a vector defined by a column of a primary upmix matrix;
• selecting at least one eigenvector from the plurality of eigenvectors based on the subspace angle and a preset threshold angle θmin;
• defining at least one column of an auxiliary upmix matrix by the at least one selected eigenvector;
• and processing the input audio signal into the output audio signal (149) using an upmix matrix, wherein the upmix matrix comprises the primary upmix matrix and the auxiliary upmix matrix.