With the introduction of narrowband ISDN, low cost video telephony bit rates lower than 48 kbps, the minimum bit rate of G.722 , are needed for wideband speech. One approach has been to use 32kbps adaptive transform coding with Huffman coding, perceptually based noise shaping and dynamic bit allocation. Recently most efforts have gone into reducing the bit rate even further to 16 kbps and below, at the expense of higher delay with the intention of maximizing the signal bandwidth that can be accommodated at that bit rate [1,4].
Table 4: MOS values of 16 kb/s wideband speech coder.