Qualitative Aspects of the Voice Signal

Abstract

Of all the studies referenced in Chapters. 1 and 3, the majority have found positive correlations between various profile parameters and voice quality. The word "quality" is very loosely used in the context of audio processing. For example, one may refer to "perceptual quality," "speech quality," "audio quality," "recording quality" etc. These usages must not be confused with the subject at hand-voice quality. From both signal processing and information theoretic perspectives, voice quality is an elusive entity. There is no consensus in the scientific community about its precise definition-quantitatively or even in a descriptive sense. It is in fact a complex entity that comprises a set of many (mostly) subjectively described characteristics, or sub-qualities that collectively represent it. These characteristics, or attributes of voice, give it its particular auditory flavor, and can also be thought of as comprising the overall quality of someone's voice in a manner analogous to a sound mixer used in music production. Unfortunately, there is no consensus on even the number of sub-qualities that comprise voice quality. Regardless, some important ones are described in this chapter. This chapter also touches upon the subject of voice disguise, which is almost entirely a game of emulating and/or masking voice quality. Voice disguise is also revisited in Chap. 7 from a computational profiling perspective. 6.1 Voice Quality in Broad Perspective At the outset, it is important to differentiate between the quality of voice, the quality of the voice signal, and its intelligibility. The phrase "quality of the voice signal" refers to the fidelity of the signal capture, storage and transmission processes in preserving the information content of the original analog signal. Speech intelligibility (often loosely referred to as "quality of speech") relates to the understandability of its content and the discriminability of the sounds in it-criteria that are of importance in many speech applications, such as transmission and communication of voice through telephone and wireless channels that cut off much of its higher spectral components.