A new model-based algorithm for optimizing the MPEG-AAC in MS-stereo

Olivier Derrien (1, 2) , Gael Richard (3, 4)

1 UTLN - Université de Toulon
2 LMA - Laboratoire de Mécanique et d'Acoustique [Marseille]
3 TSI - Département Traitement du Signal et des Images
4 LTCI - Laboratoire Traitement et Communication de l'Information

In this paper, a new model-based algorithm for optimizing the MPEG-Advanced Audio Coder (AAC) in MS-stereo mode is presented. This algorithm is an extension to stereo signals of prior work on a statistical model of quantization noise. Traditionally, MS-stereo coding approaches replace the Left (L) and Right (R) channels by the Middle (M) and Sides (S) channels, each channel being independently processed, almost like a monophonic signal. In contrast, our method proposes a global approach for coding both channels in the same process. A model for the quantization error allows us to tune the quantizers on channels M and S with respect to a distortion constraint on the reconstructed channels L and R as they will appear in the decoder. This approach leads to a more efficient perceptual noise-shaping and avoids using complex psychoacoustic models built on the M and S channels. Furthermore, it provides a straightforward scheme to choose between LR and MS modes in each subband for each frame. Subjective listening tests prove that the coding efficiency at a medium bitrate (96 kbits/s for both channels) is significantly better with our algorithm than with the standard algorithm, without increase of complexity.

Mots clés: codage audio; MPEG AAC; quantification

Domaines: Traitement du signal et de l'image [eess.SP]; Traitement du signal et de l'image [eess.SP]

Olivier Derrien, Gael Richard. A new model-based algorithm for optimizing the MPEG-AAC in MS-stereo. IEEE Transactions on Audio, Speech and Language Processing, 2008, 16 (8), pp.1373-1382. ⟨10.1109/TASL.2008.2002068⟩. ⟨hal-00467510⟩