Abstract
As of today, the lion’s share of the worldwide (fixed and mobile) telephone connections is still restricted to audio frequencies below 4 kHz, leading to the familiar sound character of “telephone speech.” Meanwhile, several coding standards for “High-Definition” (HD) telephony are available which offer a significantly better audio quality and speech intelligibility. However, the required costly and time-consuming modifications of the existing network equipment turned out to be a major obstacle for their introduction. Consequently, a long transition period from today’s plain old telephony towards future HD voice networks can be expected.
To account for this situation, in this thesis, concepts, methods and algorithms are investigated, evaluated, and compared that facilitate a major audio quality upgrade of existing speech communication systems while maintaining backwards compatibility with the installed infrastructure.