To enable synchronous playback of video and audio recordings, click theicon in the upper-right corner of the frame. After this the icon looks like this and audio recording is played back synchronously with video recording in the archive playback mode.
To disable synchronous playback of video and audio recordings, click the icon. The icon will look like this and video recording will be played back with no sound.
Absence of the icon means that camera is not configured for recording audio to the archive.
To get information on configuring synchronous playback of video and audio recordings see the Configuring audio signals playback using the video monitor section of the Administrator's Guide.