An embedded variable bit-rate coder based on GSM EFR: EFR-EV

This paper describes a 12.2-32 kbps scalable wideband speech and audio coder interoperable with GSM enhanced full-rate (EFR). This coder, referred to as EFR-EV, is designed using the ITU-T G.729.1 multi-stage coding structure. Specifically, EFR-EV consists of three stages: a code-excited linear prediction (CELP) stage derived from EFR, time-domain bandwidth extension (TDBWE), and time-domain aliasing cancellation (TDAC). In this paper, we show that the G.729.1 extension layers (i.e. TDBWE and TDAC) are quite generic for scalable codec design in the sense that they can be applied to EFR with limited adjustments. In addition, we propose a minor modification of the bit allocation procedure in TDAC stage, exploiting spectral masking only for higher frequency bands. The performance of EFR- EV and G.729.1 are evaluated in terms of objective/subjective quality, algorithmic delay, and complexity.