Bandwidth extension of speech signals (Q950065)

The authors discuss the problem of quality enhancement of speech signals bandlimited by telephone networks with and without the presence of noise. Beside basics of the theory and methods for bandwidth extension, new solutions valid for real-world signals and environments comprising various kinds of disturbances are presented. The work contains results obtained during the preparation of a PhD thesis defended by the first author and is structured on seven chapters. After a short introduction, in the second chapter speech generation together with the basic approach for bandwidth extension are presented. The third chapter contains analysis techniques for speech signals: linear predictive analysis, parametric representation of the spectral envelope, scalar speech features and distance measures. Chapter four deals with the envelope extraction, estimation of the narrowband excitation signal, its extension and with finding the gain factor for performing a power adjustment. The next chapter, entitled Broadband Spectral Envelope Estimation contains methods for estimating the broadband spectral envelope based on the narrow one using codebooks, neural networks and linear mapping approaches. The training set has been prepared using a head and torso simulator in an anechoic chamber. Chapter six deals with the quality evaluation of different approaches for extending the excitation signal and estimating the broadband spectral envelope. Both subjective and objective method are discussed. The last chapter is a summary of the topics covered in the book and is followed by several appendices. For the interested reader the book is worth reading since it covers together with basic aspects related to speech processing clearly described new results and techniques with the special feature that they can be optionally used without changing the existing hardware.