Influence of the LPC filter upon the perception of breathiness and vocal effort

According to the source-filter paradigm, the perception of breathiness and vocal effort should be primarily controlled by the glottal source and be little affected by the formant filter. This experiment investigates whether the formant filter estimated by linear prediction (LPC) can influence the perception of breathiness and vocal effort. The experiment starts with a pair of voice samples. One sample exhibits high effort and the other sample exhibits breathiness. LPC estimates a filter and residual for each sample. The influence of the residual is eliminated by providing both filters with the same artificial source during resynthesis. The synthesized samples differ only according to the difference between the two filters. Three pairs of samples were evaluated by seven people in listening tests. The results demonstrate that the LPC filters do influence the perception of breathiness and vocal effort. When a voice changes between breathiness and vocal effort, the spectral envelope changes. This change is captured by the LPC filter rather than the residual. A closer look at the LPC algorithm provides an explanation for this result. 1