speaking Rate
Parameters
value
Optional. Speaking rate/speed, in the range 0.25, 4.0. 1.0 is the normal native speed supported by the specific voice. 2.0 is twice as fast, and 0.5 is half as fast. If unset(0.0), defaults to the native 1.0 speed. Any other values < 0.25 or 4.0 will return an error.