In the previous chapters exemplary processes for analyzing different aspects of voice and speech quality were presented. The stimuli used were both natural and synthesized speech sounds. The measurements were carried out with totally different aims in mind. They were introduced here to give an overall impression of the processes and aims of measurements. The processes were mainly developed for the field of speech technology. In this chapter, however, open questions and aspects that are thrown up by these measurements will be discussed.

As is clear from previous chapters, there are a number of useful studies on specific aspects of speech quality. Many, however, do not go beyond elementary single events because their positions within the field of speech quality measurements cannot be defined. This is because there is no single comprehensive concept for speech quality measuring and no corresponding structure available in which results of measurements could be classified.

This chapter seeks to redress this omission by working out a conceptual structure for speech quality measuring. The basis of this will be the discussions that have so far taken place. All those aspects and components of speech quality will now be systematically examined, i.e. they will be given an order and structure. In this concept the single components will be created and ordered in such a way that any change to one of them will affect speech quality as a whole. There will be named the most important coordinates and their mutual dependencies that are essential for describing the...