High-quality speech coding at 2.4 to 4.0 kbit/s based on time-frequency interpolation

The author presents a novel algorithm for high-quality coding and demonstrates the advantage of the proposed coder over the conventional CELP (code-excited linear prediction) algorithm for low rate coding. He proposes an empirical but perceptually advantageous framework for voice speech processing, called time-frequency interpolation (TFI). The general formulation of the TFI technique is given and then a TFI speech coder is described. The performance of this coder at 4.05 and 2.5 kbit/s is demonstrated in terms of formal MOS (mean opinion score) scores. It is shown that the 4.05 kbit/s TFI coder is comparable in performance with the 8 kbit/s European standard GSM (Group Special Mobile) coder. It is also shown that reducing the bit rate to 2.50 kbit/s only gracefully degrades the performance and the coder delivers good-quality speech at this rate.<>