Available since version: Gideros 2011.6
Sets the sound which is played when notification is shown.
By default no sound is played and if you want to play default system sound, then you can use Notification.DEFAULT_SOUND
For cross-platform compatability it is better to use .wav file types.
For IOS the audio length can not exceed 30 seconds
You can reference this IOS notification guide for converting sound to needed formats on IOS.