ABSTRACT
This chapter discusses the important aspects of language and speech which are fundamental to the development of most systems of communication, and looks briefly at some accidents involving deficiencies in this aspect of human factors. Different voices utilise different basic ranges of pitch or frequency. For the same spoken words, the general visible pattern of the speech remains recognisable for all accents and all voices. This has a relevance to speech intelligibility, because although there are many ways in which speech can be deformed, so long as the pattern of frequencies is not destroyed the speech will remain intelligible. Under most noisy conditions, ear protection worn by a listener does not degrade speech intelligibility because the signal-noise ratio remains the same. In certain cases, such as with intense noise, speech intelligibility is actually improved. Early speech intelligibility testing was costly, time consuming and involved problems of subjectivity.
