Digital telephony is now being introduced in the Public Switched Telephone Network (PSTN) at an increasing speed. Since the 1960s, digital transmission in the PSTN has been synonymous to 64kbit/s, A-law PCM (see Recommendation G.711). Now the combination of better knowledge in signal processing techniques and advances in technology, most notably LSWLSI techniques, has lead to an increased interest in more efficient coding methods than PCM. One example of this development is the introduction of 32 kbit/s ADPCM (see Recommendation G.726). More recently a 64 kbit/s, 7kHz wideband codec has been standardized by the CCITT (see Recommendation G.722).
ITU-T P.83 SPANISH-1993 history
1993ITU-T P.83 SPANISH-1993 SUBJECTIVE PERFORMANCE ASSESSMENT OF TELEPHONE-BAND AND WIDEBAND DIGITAL CODECS