Sound Channel

Scope

• Book Page content object > Audio object > Sound Channel property

Purpose

Enable Now allows multiple sound elements to be played at the same time, as long as each of them is played in a separate sound channel. As soon as one sound element is played in a channel, it will replace all other audio in that channel, but sound in all other channels will still be heard. The Sound Channel property specifies in which channel the sound for the parent Audio object should be played. This can be one of the following:

• Book Sound: Audio files assigned to this channel are played regardless of which Book Page is currently displayed on the screen (whereas all other categories apply only to the page on which the audio objects are placed). It is therefore suitable for background music. Note that you still assign Book Sound audio to a Book Page, and not to a Book. If it truly should be heard throughout the entire period the Book is displayed, you should attach the include it via the first Book Page in the Book.
• Page Sound: This channel is the primary channel for Book Pages. If you provide narrative audio via the Page Sound property (described above) then it will be assigned to this layer. Although you can assign supplemental audio to this channel, any narrative audio provided via the Page Sound property will take precedence and any supplemental audio on the channel will be ignored.
• Explanations: This channel should be used for additional—possibly optional—narrative that is not included in the main Page Sound. A typical use case would be narrative that is only played in response to a user action (for example, providing additional explanation when the user hovers over an object on the screen).
• Effects: This channel should be used for ‘sound effects’.
• Others: This channel can be used for anything not covered by the previous categories.

Having multiple channels allows you to effectively ‘layer’ sound—for example, having background music playing throughout a Book, an audio narrative (voiceover) playing on each individual Book Page, and then sound effects playing when they are triggered by certain events on the Book Page (for example, playing a ‘click’ sound when the user clicks on an object on the page.

When deciding which channels to use for what purpose, you may find it useful to consider the controls available to the user for controlling sound levels in the Book Reader.