High quality 16 kb/s voice transmission: The subband coder approach

This paper describes a high quality 16 kb/s subband coder using quadrature mirror filters (QMF). In this algorithm, the partitioning of the speech band into subbands is performed via a bank of eight bandpass filters whose coefficients are derived from a QMF tree structure. Due to the special properties of the QMF, no significant spectral distortions are introduced in the band-splitting and reconstruction processes. To enable a more efficient encoding of the subband waveforms, an adaptive bit assignment scheme is incorporated which allocates the number of quantizer bits according to the distribution of subband energies.