Exploring the characteristics of analytic decomposition of speech signals

This paper investigates the properties of analytic transformation of speech into envelope and phase functions. The envelope is shown to evolve slowly with the pitch of the input speech, whilst the phase consists of two components; one evolving slowly with pitch and another that exhibits a more rapid evolution. We investigate decomposing the phase component further using two distinct methods: (a) filtering of the phase in the pitch evolutionary direction and (b) performing a second analytic decomposition of the phase into secondary envelope and phase components. To examine the characteristics of the pitch cycle evolution, the analytic transform is employed in a waveform interpolation (WI) coding structure. The two phase decompositions are then analysed with particular emphasis on quantisation sensitivity and the required transmission rate. Results indicate that the analytic decomposition may offer a degree of scalability to speech coders, especially when employed in coders that exploit pitch evolution such as WI.