Modulation transfer function design for a flexible cross synthesis VOCODER based on F0 adaptive spectral envelope recovery

A new design procedure for flexible cross synthesis VOCODER is proposed based on TANDEM-STRAIGHT framework, a F0 adaptive spectral envelope estimator, and modulation transfer function design. The proposed design procedure enables control of speech intelligibility and timber identity of musical instruments or animal voices. Removal of the averaged and smoothed logarithmic spectrum of speech from the filter reduced the timbre modification effect of filtered sounds and manipulation of cut-off frequencies of modulation transfer function for designing the filter enabled control of trade-offs between intelligibility and timbre preservation.