Real-time implementation of a 9600 bps subband coder with time-domain harmonic scaling

This paper describes the real-time implementation of a high quality 9600 bps speech coder on the microprocessor based GTE MARK IV voice digitizer. The speech processing technique programmed is a combination of the subband coding (SBC) with the Time-Domain Harmonic Scaling (TDHS) algorithm. The SBC employs a bank of eight quadrature mirror filters to partition the speech bandwidth into subbands. An adaptive bit allocation scheme is incorporated to assign the quantizer bits dynamically according to the energies of the subband waveforms. The TDHS technique is included as a pre-and post-processors to the SBC. By exploiting the periodic nature of the voiced speech, the scheme compresses and Later expands the frequency range of the input waveform. Though at the expense of pitch calculations and some overhead multiplication, the TDHS reduces the processing requirements of SRC by a factor of two. Forward error correcting codes are also included to improve the robustness of the speech coder to channel coders.