16 kbit/s wideband speech coding based on unequal subbands

We propose a split-band encoding scheme for 16 kbit/s wideband speech coding (50-7000 Hz), using 2 unequal subbands from 0-6 kHz and from 6-7 kHz. This approach was motivated by an experimental evaluation of the signal bandwidth of speech frames. The higher subband is simply represented by white noise with adjustment of the short term energy. For the lower subband code-excited linear prediction (CELP) is used. The analysis filter bank, which performs the unequal band splitting combined with critical subsampling of the sub-bands, is described. A bit error concealment technique and the bit allocation is also presented. By informal listening tests the speech quality was rated higher than the speech quality of the CCITT G.722 wideband codec operating at 48 kbit/s.