CSS voice-volume

The CSS voice-volume property is used in speech media for controlling the amplitude of the audio waveform generated by the speech synthesiser.

The voice-volume property can also be used for adjusting the relative volume level of audio cues within the aural box model of the selected element.

You can use the voice-volume property to adjust the volume level of spoken content when the content is being read out by a device such as a screen reader.

Syntax

Possible Values

decibel

A number followed by dB (decibel unit identifier).

This represents a change (positive or negative) relative to the given keyword value, or to the default value for the root element, or otherwise to the inherited volume level (which may itself be a combination of a keyword value and of a decibel offset, in which case the decibel values are combined additively).

silent

No sound at all. The content is read silently. Therefore, the selected element takes up the same time as if it is being read out loud. To prevent this, set the speak property to none.

x-soft, soft, medium, loud, x-loud

These keywords are mapped to values determined by the user agent that meet the listener's requirements with regards to perceived loudness. Generally, the user can customize these base values via their preferences (or similar interface) in a way that's suitable to their auditory environment.

In addition, all CSS properties also accept the following CSS-wide keyword values as the sole component of their property value:

initial

Represents the value specified as the property's initial value.

inherit

Represents the computed value of the property on the element's parent.

unset

This value acts as either inherit or initial, depending on whether the property is inherited or not. In other words, it sets all properties to their parent value if they are inheritable or to their initial value if not inheritable.

General Information

Example Code

Official Specifications

• CSS Speech Module (W3C Candidate Recommendation 20 March 2012)

Vendor Prefixes

For maximum browser compatibility many web developers add browser-specific properties by using extensions such as -webkit- for Safari, Google Chrome, and Opera (newer versions), -ms- for Internet Explorer, -moz- for Firefox, -o- for older versions of Opera etc. As with any CSS property, if a browser doesn't support a proprietary extension, it will simply ignore it.

This practice is not recommended by the W3C, however in many cases, the only way you can test a property is to include the CSS extension that is compatible with your browser.

The major browser manufacturers generally strive to adhere to the W3C specifications, and when they support a non-prefixed property, they typically remove the prefixed version. Also, W3C advises vendors to remove their prefixes for properties that reach Candidate Recommendation status.

Many developers use Autoprefixer, which is a postprocessor for CSS. Autoprefixer automatically adds vendor prefixes to your CSS so that you don't need to. It also removes old, unnecessary prefixes from your CSS.

You can also use Autoprefixer with preprocessors such as Less and Sass.