How to stop mechanized (robot) voice when "playback speed" is increased or decreased?

[cadu]

Hi,

I need to deal with increased and decreased "playback speed" (shortcuts C or X). But when the voice isn't in normal speed, it changes to a mechanized (robot) voice. Does anyone know how to stop mechanized (robot) voice when "playback speed" is increased or decreased? I tried changing all options of "audio => speech processing" but nothing could remove the robot voice!

Thanks in advance,
Cadu