Spatial parameters for audio coding: MDCT domain analysis and synthesis
We use Modified Discrete Cosine Transform (MDCT) to analyze and synthesize spatial parameters. MDCT in itself lacks phase information and energy conservation, which are needed by spatial parameters representation. Completing MDCT with Modified Discrete Sine Transform (MDST) into MDCT-j*MDST overcomes this and enables the representation in a form similar to that of DFT. And due to overlap-add in time domain, a MDST spectrum can be built perfectly from MDCT spectra of neighboring frames through matrix-vector multiplication. The matrix is heavily diagonal and keeping only a small number of its sub-diagonals is sufficient for approximation. When using MDCT based core coder in spatial audio coding, like Advanced Audio Coding (AAC), we need no separate transforming for spatial processing, cutting down significantly the computational complexity. Subjective listening tests also show that MDCT domain spatial processing has no quality impairment.
spatial parameter audio coding mdct mdst singular value