Property Reference - CSS Reference - page 309

Name
voice-rate
Values:
<percentage> | x-slow | slow | medium | fast | x-fast
Initial value:
medium
Applies to:
All elements
Inherited:
Yes
Percentages:
Refer to the default value
Computed value:
Not specified (in the previous incarnation, speech-rate , it was an absolute number)
Description:
Defines the average rate at which words are spoken when an element's content is audibly
rendered.
Examples:
h1 {voice-rate: 33%;}
.legalese {voice-rate: x-fast;}