Manipulating tracheoesophageal speech

Speech therapy aiming at improving voice quality and speech intelligibility is often hampered by the lack of knowledge of the underlying deficits. One way to help speech therapists treating patients would be to supply synthetic benchmarks for pathological
speech. These can be used to train therapists and evaluate and interpret automatic speech recognizers used for diagnosing pathological speech. Moreover, synthetic pathological speech can also be used to make expected therapy aims audible before
treatment. In a listening experiment testing perceived intelligibility, three types of manipulations of tracheoesophageal speech were evaluated by experienced speech therapists. It was found that modeling the intensity contour of the voice source signal improved speech quality over plain analysis-synthesis. Replacing the voicing source with fully synthetic source periods decreased the perceived intelligibility markedly. Making the
source fully periodic with a regular pitch had no effect on perceived intelligibility. Low quality speech benefitted more from manipulations, or deteriorated less, than high quality speech.