I have updated Keyboard Maestro to the very last version 9.0.2 and although I can't 100% affirm this (since I haven't used that function in a few weeks), I feel like the "Speak Text" with "Samantha" voice is totally different and very unpleasant. Have you changed anything or is it OS related?
I just tried Samantha two ways:
-
In Safari using Edit > Speech > Start Speaking on a selection
-
Using the Keyboard Maestro Speak Text action on the same text
Both were identical (High Sierra) and not unpleasant or clipped. You might take a look at System Preferences > Accessibility > Speech to confirm Samantha is active and, while there, test it.
Sorry I can't be more help.
Oh no you have helped, thank you. Indeed they are identical in KM and in the system, so I believe Apple has changed it in Mojave then (I used to have High Sierra and updated quite recently). Cheers!