Modification of energy spectra, epoch parameters and prosody for emotion conversion in speech

This work attempts to convert a given neutral speech to a target emotional style using signal processing techniques. Sadness and anger emotions are considered in this study. For emotion conversion, we propose signal processing methods to process neutral speech in three ways: (i) modifying the energy spectra (ii) modifying the source features and (iii) modifying the prosodic features. Energy spectra of different emotions are analyzed, and a method has been proposed to modify the energy spectra of neutral speech after dividing the speech into different frequency bands. For the source part, epoch strength and epoch sharpness are extensively studied. A new method has been proposed for modification and incorporation of epoch strength and epoch sharpness parameters using appropriate modification factors. Prosodic features like pitch contour and intensity have also been modified in this work. New pitch contours corresponding to the target emotions are derived from the pitch contours of neutral test utterances. The new pitch contours are incorporated into the neutral utterances. Intensity modification is done by dividing neutral utterances into three equal segments and modifying the intensities of these segments separately, according to the modification factors suitable for the target emotions. Subjective evaluation using mean opinion scores has been carried out to evaluate the quality of converted emotional speech. Though the modified speech does not completely resemble the target emotion, the potential of these methods to change the style of the speech is demonstrated by these subjective tests.