pitch

The pitch property allows you to specify the average pitch of a speaking voice in hertz (Hz) or Kilohertz (KHz) . For example:

p {pitch: 120Hz}
p {pitch: low}

Each voice family has a different average pitch but the average male frequency is 120Hz and the average female frequency is higher at 210Hz. Of course, this varies from speaker to speaker, and children's voices are much higher.

When you choose a voice using the voice-family property, you also implicitly choose the average pitch for your document. If you don't like the pitch of the voice, you can use the pitch property to alter it.

If you provide a numeric value for this property, the browser produces the voice with the pitch you specify. This may work, but you may also be shift your voice to a pitch that makes it difficult to understand or unintentionally amusing.

You might be better off to specify a frequency as x-low, low, medium, high or x-high and let the browser alter the pitch of the voice family to a corresponding new frequency. However, the browser must map the values in order (x-low is a lower frequency than low and so on). In any case, you are more likely to get a voice with a pitch that sounds good and works well with your chosen voice family.