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AC3/DTS audio on non-AC3/DTS system...

4539 Views 16 Replies Latest reply: Dec 28, 2009 10:59 PM by KevinD RSS
  • I Dylan Malone Level 1 Level 1 (15 points)
    Currently Being Moderated
    Dec 28, 2009 7:32 PM (in response to Chenks)
    I've been having a heck of a time getting Dolby Digital 5.1 to work from my AppleTV over HDMI (though the video works fine). Unless I use an optical cable to carry the audio it seems to only see the stereo audio track. It's would be only an annoyance to run the extra cable, except that I have a lot of devices in my home theater, and using up the optical input needlessly causes other problems for me.

    Are you certain that DD5.1 is passed through over HDMI? My reasonably expensive / new / feature-packed home theater receiver seems convinced that it gets only stereo via HDMI with this device. (My PS3 and other devices happily send DD5.1 and other more exotic surround sound formats via HDMI, it's just the AppleTV that seems to misbehave).
    Mac Pro (Intel), Mac OS X (10.5.8)
  • KevinD Level 1 Level 1 (5 points)
    Currently Being Moderated
    Dec 28, 2009 10:59 PM (in response to kristin.)
    Kristin, here is the answer to your original question: When you encode the 5.1 (AC-3 or DTS) as the only audio file for the TV, you are not encoding the 5 discrete channels. You are encoding the front left & right channels. The left & right surround & the center channel are not encoded. That center channel contains the dialog track which for most movies are over 70% of the audio. That is why the dialog is so muted in your encoded movies. As is mentioned in the responses, you should always encode a down-mixed audio track from these sources (AC-3 stereo or ProLogic/ProLogicII). That down-mix will include the all important center channel as well the surrounds. If want 5.1 sound later, then you will need to include the 5.1 tracks as a pass-thru. Not an encode. What that means is you are including the digital stream as a separate file needed for a 5.1 decoder to work on. Those decoders are only found on HT receivers and in some DVD/BR players. They are not built into the TV or most (all?) HDTVs. That is why it is called a pass-thru. It is not an audio file that the TV or HDTV can convert to sound and is ignored by their audio processors. But it is not eliminated and is always there. You don't want to "encode" 5.1 tracks as-is or you will lose the center & surround channels. You want to encode a down-mixed soundtrack (stereo/DPL/DPL II) for stereo playback on a TV or basic stereo and include a pass-thru of the intact AC-3/DTS digital bitstream for later use on a 5.1 home theater receiver. Handbrake can do that. And as far as I know the only way to pass that 5.1 bitstream to a receiver is using the optical audio out on the TV. Not sure if the HDMI connection will pass 5.1 bitstreams. It might, BUT be aware that many basic home theater receivers with HDMI connectivity only accept video signals through those jacks. Not audio. You may have to use the optical jacks for that anyway.
    Early 2009 Mac Mini, iBook G4 1.33, ATV, AEBS (802.11n), AX (802.11n), Mac OS X (10.5.6)
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