Variable-size vector entropy coding of speech and audio

Many modern analog media coders employ some form of entropy coding (EC). Usually, a simple per-letter EC is used to keep the coder's complexity and price low. In some coders, individual symbols are grouped into small fixed-size vectors before EC is applied. We extend this approach to form variable-size vector EC (VSVEC) in which vector sizes may be from 1 to several hundreds. The method is, however, complexity-constrained in the sense that the vector size is always as large as allowed by a pre-set complexity limit. The idea is studied in the framework of a modified discrete cosine transform (MDCT) coder. It is shown experimentally, using diverse audio material, that a rate reduction of about 37% can be achieved. The method is, however, not specific to MDCT coding but can be incorporated in various speech, audio, image and video coders.