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.
Optional volume gain (in dB) of the normal native volume
supported by the specific voice, in the range [-96.0, 16.0].
If unset, or set to a value of 0.0 (dB), will play at normal
native signal amplitude. A value of -6.0 (dB) will play at
approximately half the amplitude of the normal native signal
amplitude. A value of +6.0 (dB) will play at approximately
twice the amplitude of the normal native signal amplitude.
Strongly recommend not to exceed +10 (dB) as there's usually
no effective increase in loudness for any value greater than
that.
An identifier which selects 'audio effects' profiles that are
applied on (post synthesized) text to speech. Effects are
applied on top of each other in the order they are given.