Hoelper, Carsten; Vary, Peter (Institute of Communication Systems and Data Processing, RWTH Aachen University, Germany)
Today’s speech coding and transmission systems are either analogue or digital, with a strong shift towards digital during the last decades. We combine digital and analogue schemes for the benefit of saving transmission bandwidth, complexity, and of improving the achievable speech quality at any given signal-to-noise ratio (SNR) on the channel. The combination is achieved by transmitting analogue samples of the unquantized residual signal of a linear predictive digital filter. The new system, Mixed Pseudo Analogue-Digital (MAD) transmission, is applied to narrowband and wideband speech. MAD transmission over a channel modeled by additive white Gaussian noise (AWGN) is compared to the GSM Adaptive Multi-Rate speech codec mode 12.2 kbit/s, which uses a comparable transmission bandwidth if channel coding is included. A wideband extension scheme for the low-pass filtered residual is introduced to further reduce the transmission bandwidth.