Implementation of the CCITT wideband coder using a high performance, fixed point DSP
Yhean-Sen Lai, J. Hartung · 2003
In 1986 CCITT (International Telegraph and Telephone Consultative Committee) Study Group XVII recommended an international standard for coding wideband speech and music (50-7000 Hz) at 64 Kb/s or less. Some applications envisioned for such a coder are in teleconferencing, commentary channels, and for use in high-grade telephones for ISDN (integrated-services digital network) applications. The authors describe a full-duplex implementation of this algorithm on a single AT&T WE DSP16 digital signal processor (DSP) running at a 55 ns instruction-cycle time. An AT&T T7521 codec is used to digitize the analog signal with 15-bit precision at a 16 kHz sample rate. The codec provides both antialiasing and reconstruction filters on-chip. The codec interfaces directly to the DSP16 serial port, and data are double-buffered in hardware, and transferred into on-chip RAM using the interrupt facility on the DSP device. The parallel port of the device is used for both controlling program execution and interfacing to a 192 kb/s serial bit-stream.>