On the Design of Sub-band Coders for Low-Bit-Rate Speech Communication

This paper presents a detailed discussion of issues involved in the design of sub-band coders for low-bit-rate speech communications. Specifically, bit rates in the range of 7.2 to 16 kb/s are emphasized. Design guidelines, based on results of extensive computer simulations and subjective comparisons, are presented for selection of sub-band coder parameters. Practical considerations for selecting sub-bands under integer-band sampling and multiplexing constraints are also discussed, and a method for synchronous multiplexing of the sub-band data, without buffering, is proposed. Several examples of sub-band coders for transmission rates of 7.2, 9.6, and 16 kb/s are presented, and the quality of these coders is compared against that of adpcm and adm coders.