Signal-adaptive transform kernel switching for stereo audio coding

Modern stereo and multi-channel perceptual audio codecs utilizing the modified discrete cosine transform (MDCT) can achieve very good overall coding quality even at low bit-rates but lack efficiency on some material with inter-channel phase difference (IPD) of about ±90 degrees. To address this issue a generalization of the lapped transform coding scheme is proposed which retains the perfect reconstruction property while allowing the usage of three further transform kernels, one of which is the modified discrete sine transform (MDST). Blind listening tests indicate that by frame-wise adaptation of each channel´s transform kernel to the instantaneous IPD characteristics, notable gains in coding quality are possible with only negligible increase in decoder complexity and parameter rate.