Starting at the top, DRC stands for "Dynamic Range Compression". What this adjustment does, when activated, is decrease the difference between the loudest and softest parts of a soundtrack. This is practical for two reasons: First, this helps to make dialog louder in relation to the special effects, and, second, enables one to listen at lower volumes and still hear both the dialog and effects adequately. This is great for late night DVD viewing or CD listening.
The AV synch function adjusts the timing between the video and audio. On some DVD and TVs there is sometimes an audio/video delay, which results in the soundtrack being out of synch with the video. By putting the audio and video back in balance, you may avoid watching what seems like a poorly-dubbed movie.
The HDMI audio function determines whether you want the audio from DVD player to the TV or to remain in the HT-X810. If you select HDMI ON, the audio comes out of your TV. The preferred position is Off - so you can hear the audio as it comes through the HT-X810 main unit and subwoofer.
