W3cubDocs

/Web APIs

SpeechSynthesisUtterance: rate property

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

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
rate 33 14 49 No 21 7 No 33 62 No 7 3.0

See also

© 2005–2023 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/SpeechSynthesisUtterance/rate