SpeechSynthesisUtterance: rate property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2018.

The rate property of the SpeechSynthesisUtterance interface gets and sets the speed at which the utterance will be spoken at.

If unset, a default value of 1 will be used.

Value

A float representing the rate value. It can range between 0.1 (lowest) and 10 (highest), with 1 being the default rate for the current platform or voice, which should correspond to a normal speaking rate. Other values act as a percentage relative to this, so for example 2 is twice as fast, 0.5 is half as fast, etc.

Some speech synthesis engines or voices may constrain the minimum and maximum rates further. If SSML is used, this value will be overridden by prosody tags in the markup.

Examples

Adjusting playback rate

In this example we can adjust the playback rate using the slider, then play the utterance with the "Play" button.

HTML

html
<p id="text">It was a dark and stormy night.</p>

<div id="rate-control">
  <label for="rate">Rate:</label>
  <input type="range" min="0.5" max="2" value="1" step="0.1" id="rate" />
</div>

<button id="play">Play</button>

CSS

css
body {
  font-family: sans-serif;
}

#rate-control {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin: 1rem 0;
}

JavaScript

js
const synth = window.speechSynthesis;

const text = document.querySelector("#text");
const play = document.querySelector("#play");
const rate = document.querySelector("#rate");

function speak() {
  if (synth.speaking) {
    synth.cancel();
  }
  const utterThis = new SpeechSynthesisUtterance(text.textContent);
  utterThis.addEventListener("error", () => {
    console.error("SpeechSynthesisUtterance error");
  });
  utterThis.rate = rate.value;
  synth.speak(utterThis);
}

play.addEventListener("click", speak);

Output

Specifications

Specification
Web Speech API
# dom-speechsynthesisutterance-rate

Browser compatibility

BCD tables only load in the browser

See also