Selection of a PCM coder for digital switching

Selection of a coder for digitizing speech and subsequent processing inside a digital switch is virtually dictated by existing analog and digital trunks with which the switch is to interface, by system requirements on signal-to-noise ratio (SNR), idle channel noise (ICN), dynamic range (DR), and by CCITT specifications. To facilitate the selection, this paper compares four coders, namely, 13-bit and 14-bit uniform (linear), A-law¹, and μ-law²coders on the basis of SNR, ICN, DR, and the distortion introduced by code conversions-from linear to companded and vice versa. It is shown that a 13-bit midtread coder outperforms both A-law and μ-law coders and that it is a good choice for digital switching systems.