A Fixed Rate Speech Coder with Improved Database Search

The Adaptive Multi-rate Speech Coder

In this paper, we describe the Adaptive Multi-Rate (AMR) speech coder currently under standardization for GSM systems as part of the AMR speech service. The coder is a multi-rate ACELP coder with 8 modes operating at bit-rates from 12.2 kbit/s down to 4.75 kbitls. The coder modes are integrated in a common structure where the bit-rate scalability is realized mainly by altering the quantization ...

A 2.4 kbps variable bit rate ADP-CELP speech coder

This paper presents a variable bit rate ADP-CELP (Adaptive Density Pulse Code Excited Linear Prediction) coder that selects one of four kinds of coding structure in each frame based on short time speech characteristics. To improve speech quality and reduce the average bit rate, we have developed a speech/non-speech classification method using spectrum envelope variation, which is robust for bac...

A low bit rate speech coder based on Gaussian adaptivewaveletsShubha

A low bit rate speech coder based on Gaussian adaptive wavelets is described. This speech coder ameliorates the problem of using two diierent mother wavelets to model voiced and unvoiced sounds as mentioned in. 1 In addition, it has been demonstrated in this paper, that Gaussian adaptive wavelets are better suited to model both voiced and unvoiced sounds as compared to Morlet and Daubechies' wa...

Enhancing Speech Coder Quality: Improved Noise Estimation for Postfilters

ITU-T G.711.1 is a multirate wideband extension for the well-known ITU-T G.711 pulse code modulation of voice frequencies. The extended system is fully interoperable with the legacy narrowband one. In the case where the legacy G.711 is used to code a speech signal and G.711.1 is used to decode it, quantization noise may be audible. For this situation, the standard proposes an optional postfilte...

Hybrid transform coder for low bit rate speech coding