A novel codebook search technique for estimating the open quotient

The open quotient (OQ), loosely defined as the proportion of time the glottis is open during phonation, is an important parameter in many source models. Accurate estimation of OQ from acoustic signals is a non-trivial process as it involves the separation of the source signal from the vocal-tract transfer function. Often this process is hampered by the lack of direct physiological data with which to calibrate algorithms. In this paper, an analysis-by-synthesis method using a codebook of harmonically-based Liljencrants-Fant (LF) source models in conjunction with a constrained optimizer was used to obtain estimates of OQ from four subjects. The estimates were compared with physiological measurements from high-speed imaging. Results showed relatively high correlations between the estimated and measured values for only two of the speakers, suggesting that existing source models may be unable to accurately represent some source signals.