Wideband (0-7kHz) speech coding techniques
With the existing telephone networks evolving towards Integrated Services Digital Networks, there is a specific need to transmit high quality wideband (0-7 kHz) speech at 64 kbps or below for special services like voice channels in teleconferencing, commentary channels for broadcasting etc. In this thesis, a computer simulation study of digital coding of wideband speech at 64 kbps using relatively simple coding techniques is first presented. The performance of ADPCM coders employing fixed or adaptive prediction, with or without noise spectral shaping, and 2-band subband coders is examined under ideal as well as noisy channel conditions. While preserving the quality of the 64 kbps recovered speech, the transmission bit rate is reduced to 56 kbps so that 8 kbps data can be accommodated within 64 kbps channel.