Rakesh Taori

Hi-BIN: an alternative approach to wideband speech coding

In this paper, an encoding technique called Hi-BIN (High Band Injection), which can be combined with any narrowband coder to achieve good quality wideband speech, is described. The principle behind this technique is to model frequencies above 4 kHz by noise with an appropriate spectral shape. This simple way of injecting synthetic noise in the higher frequencies gives surprisingly good quality when compared to very widely used computationally intensive waveform coding techniques such as CELP. We show that Hi-BIN offers a low bit-rate representation of the higher band and is backwards compatible with existing narrowband speech coding systems.

Speech compression using pitch synchronous interpolation

This paper presents a new time-domain algorithm for compressing speech signals. Using a novel tool which we will refer to as time weighted average (TWA), a periodically extendable pitch cycle is extracted from the voiced regions in the speech signal. This procedure is carried out every x/sup th/ pitch period. The discarded x-1 pitch periods are recovered using pitch synchronous interpolation (PSI). The computational complexity of the resulting decoder is surprisingly modest and shows reasonable potential of implementation on hardware as primitive as the Intel 8088 /spl mu/-processor. Simulation results show that the reconstruction quality is comparable to G.721.

State of the art and trends in speech coding

An introductory review of some basic speech coding techniques covers the most important properties of speech production and hearing, the ubiquitous techniques of quantization and linear prediction, and a recital of the most important measures of coding performance. In the survey that follows, several standardized speech coding systems reflecting the state of the art in speech coding are discussed in terms of coding method, bit rate, performance, complexity and typical application areas. Major future trends are indicated on the basis of expected future standards. The paper, which primarily deals with narrowband speech coding systems, is concluded by a review of the state of affairs and an outline of the future trends in the area of wideband speech coding.

Transmission system with speech encoder with improved pitch detection

A transmission system contains a speech coder which utilizes a pitch detector that is arranged to select a characteristic auxiliary signal portion from the signal to be coded in order to improve the quality of the pitch detection. The pitch is found by searching in the speech signal for signal portions that correspond to the characteristics auxiliary signal portion and by calculating the time difference between the respective signal portions.

On scalability in CELP coding systems

We propose methods to achieve bit-rate and complexity scalability in CELP coders/decoders. These methods can be implemented as plug-ins or add-ons to existing CELP systems. The associated scale factors can be readjusted even during run-time. In particular, using the proposed methods, a wideband (sampling rate 16 kHz) coder/decoder has been developed that is capable of reconstructing good to high quality speech at bit rates ranging from 14 to 24 kbit/s. The possible complexity range of the decoder can amount to a factor of 2 or more, depending on the constitution of the transmitted bitstream. Although the system also incorporates a complexity scalable encoder, it is not discussed in this paper. This system has been submitted to MPEG-4, where it has been incorporated in the MPEG-4 Audio Verification Model.