With this function you can fade a group of sounds in or out over a given length of time, or it can be used to set the group gain instantly. The time is measured in milliseconds, and the function requires that you input a final level of gain for the group to have reached by the end of that time. This gain can be between 0 (silent) and 1 (full volume) and the scale is linear, such that a value of 0.5 would be half volume. To instantly change the gain, simply set the time argument to 0. Note that on some platforms you can have a gain of greater than 1, although a value of 1 is considered "full volume" and anything greater may introduce audio clipping.
audio_group_set_gain(groupID, volume, time);
|groupID||The index of the audio group to stop (as defined in the Audio Groups Window)|
|volume||The final value for the group volume.|
|time||The length of the change in gain in milliseconds.|
audio_group_set_gain(audiogroup1, 0, 5000);
The above code checks for the "space" key and then fades all the audio for "audiogroup1" down to 0 over 5 seconds.