Low-complexity Wideband Speech Coding

Wideband speech coding has been gaining popularity in recent years. Due to its higher sampling rate, wideband speech inherently requires higher processing power than telephone-bandwidth speech when the same coding algorithm is used. However, today many wideband coding applications demand a complexity that is even lower than that of most state-of-the-art telephone-bandwidth coders. To meet this complexity challenge, we created two wideband coders that are fundamentally different from and simpler than popular narrowband coders. The first one is a transform coder based on the modified discrete cosine transform (MDCT), LPC spectral fit, and pitch harmonic fit. The second algorithm is called UTransform Predictive Coding”, or TPC. It uses short-term and long-term prediction to remove the redundancy in speech. The prediction residual is quantized in the frequency domain based on a calculated noise masking threshold. In its current form, the TPC coder uses only open-loop quantization and therefore has a low complexity. We estimate that its complexity is only about half of that of the ITU-T 16 kb/s G.728 LD-CELP narrowband coder. The speech quality of TPC is almost transparent at 32 kb/s, very good at 24 kb/s, and acceptable at 16 kb/s. Work is in progress to further improve the speech quality at 16 kb/s.