CSS RICHNESS

This property specifies the richness, or brightness, of the speaking voice. Higher values of richness/brightness have rougher waveforms and tend to carry better than lower richness values with smoother waveforms.

Example
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body {
  richness: 75
}
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<body style="richness: 75">text</body>

Possible Values

inherit: Explicitly sets the value of this property to that of the parent.
[number]: This is an integer value between 0 and 100 representing the brightness of the voice. Higher values indicate a brighter voice while lower values create a softer voice.