This page focuses on making a continuum between “task” and “dask”. Below you’ll find the wav files used, as well as a prevoiced version of “dask”, for if you’d like to play around with it.
You’ll see below the temporal anchors for the morphing substrate. The main focus of the anchors is around when the burst and aspiration occur, so anchors have been placed at various points: before the burst, after the burst, when voicing begins, and when formant transitions are complete.
It could be argued that rather than placing a boundary where voicing begins, that boundary should be placed relative to the formant transitions. In “dask”, that aligns with voicing, but in “task” formant transitions begin during the aspiration. This would result in a continua centered around the source going from aperiodic to periodic, rather than the duration of the aperiodic aspiration. I’m going to leave this as a task to you if you’re interested in comparing the resulting continua. It should be less natural, because the amplitude of prevoicing would weaken as the VOT gets shorter, which doesn’t make sense from an articulatory standpoint. A potentially better way would be to create two continua next to one another, one from aspirated to unaspirated and then from unaspirated to prevoiced.
Below you’ll find the full morphed continuum from aspirated “task” to unaspirated “dask”.
One thing to note, is that due to the way STRAIGHT does its synthesis, quick transients like stop bursts can get weakened compared to their original form. If we look at the natural stop burst for “task”, we see that it is higher in amplitude than the following aspiration.
However, the same cannot be said for the synthesized version, where the burst amplitude has been reduced and is comparable to the aspiration amplitude.
In general, while STRAIGHT excels at modelling continous sources like voicing and turbulence, it’s not as good at modelling transient sources like bursts.