Andreas Johannes Gerrits

Speech enhancement via frequency bandwidth extension using line spectral frequencies

This paper contributes to narrowband speech enhancement by means of frequency bandwidth extension. A new algorithm is proposed for generating synthetic frequency components in the high-band (i.e., 4-8 kHz) given the low-band ones (i.e., 0-4 kHz) for wide-band speech synthesis. It is based on linear prediction (LPC) analysis-synthesis. It consists of a spectral envelope extension using efficiently line spectral frequencies (LSF) and a bandwidth extension of the LPC analysis residual using a spectral folding. The low-band LSF of the synthesis signal are obtained from the input speech signal and the high-band LSF are estimated from the low-band ones using statistical models. This estimation is achieved by means of four models that are distinguished by means of the first two reflection coefficients obtained from the input signal linear prediction analysis.

Low-band extension of telephone-band speech

This paper describes a system that generates a low-band signal (100-300 Hz) from a telephone-band (300-3400 Hz) speech signal to obtain an extended-band speech signal (100-3400 Hz). The low-band increases signal naturalness and listening comfort. This system is applied at the receiving end such that compatibility with all current telephone networks is maintained. The described technique splits the telephone-band speech signal into a spectral envelope and a short-term residual. The spectral envelope and the residual are extended separately and recombined to create an extended band signal. This system is evaluated by listening tests and distortion measurement.

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.

Audio coding based on frequency variations of sinusoidal components

Coding of an audio signal is provided where an indicator of the frequency variation of sinusoidal components of the signal is used in the tracking algorithm of a sinusoidal coder where sinusoidal parameters from appropriate sinusoids from consecutive segments are linked. By applying an indicator such as a warp factor or polynomial fitting, more accurate tracks are obtained. As a result, the sinusoids can be encoded more efficiently. Furthermore, a better audio quality can be obtained by improved phase continuation.

A hybrid parametric-waveform approach to bit stream scalable audio coding

In this paper we present a wideband (44.1 kHz sampling rate) audio and speech coder that combines two different strategies, namely, parametric and waveform coding. It is shown how this approach can be used to design a layered bit stream scalable coder offering a wide variety of decoding bit rates with little scalability loss. Moreover, the bit rates associated with the different layers are competitive, in terms of quality, to those of standardized coders (MP3, AAC) tuned at a particular bit rate.