Technique for encoding/decoding of codebook indices for quantized mdct spectrum in scalable speech and audio codecs

TL;DR: In this article, a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer is obtained, where the residual signal is a difference between an original audio signal and a reconstructed version of the original signal, which is then transformed at a Discrete Cosine Transform (DCT) type transform layer to obtain a corresponding transform spectrum.

Abstract: Codebook indices for a scalable speech and audio codec may be efficiently encoded based on anticipated probability distributions for such codebook indices. A residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer may be obtained, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal. The residual signal may be transformed at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum. The transform spectrum is divided into a plurality of spectral bands, where each spectral band having a plurality of spectral lines. A plurality of different codebooks are then selected for encoding the spectral bands, where each codebook is associated with a codebook index. A plurality of codebook indices associated with the selected codebooks are then encoded together to obtain a descriptor code that more compactly represents the codebook indices.