HDMI multi channel audio - any LPCM or AAC options?

O

Owen Smith

Well-Known Member
I've been using Dolby Digital out of the HDMI to my TV and then optical to my old AV amp to get 5.1 multi channel sound on the HD channels. That works fine but involves an undesirable AAC to Dolby Digital transcode in the Humax. It's never good to transcode between two lossy audio formats.

I'm getting a new AV amp that can do HDMI audio. Certainly 5.1 LPCM, and possibly AAC though that may be stereo only. I've never noticed anything in the menus, is there any way to persuade the HDR Fox T2 to output 5.1 LPCM or AAC over the HDMI? Does it negotiate with the other end to enquire its capabilities and therefore will automatically use LPCM with my new amp?
 
The options available are stereo and multi-channel. Stereo is PCM decoded from the live/recorded audio stream, but I presumed the multi-channel is simply the live/recorded audio stream as-is.
 
Black Hole said:
I presumed the multi-channel is simply the live/recorded audio stream as-is.
Click to expand...
That's pretty much the one thing it never is on any Freeview HD device. On HD channels the broadcast audio is usually in AAC, and when 5.1 sound is broadcast it's in 5.1 AAC. Almost nothing on the market can take that as a bistream and decode it and play it on a surround sound system.

There are two general options (apart from stereo downmixes):

* Freeview HD device decodes AAC and outputs 5.1 LPCM over HDMI, this is what I'd like to do with my new amp since it avoids a transcode to another lossy format.

* Freeview HD device transcodes the 5.1 AAC to Dolby Digital 5.1 at 640kbps (the max for that protocol) which can be carried on optical or coax digital out to old AV amps as well as over HDMI, and the amp then decodes that and plays it. The HDR Fox T2 uses Dolby Pulse to do this which claims to use clever frequency domain partial transcoding to avoid too much loss, but it's still better to not transcode at all.

Clearly other options are possible, likely the device transcoding to DTS 5.1 at 1.5mbps which can be carried on optical or coax digital out as well as HDMI, but the above two are the only ones that I'm aware of existing.
 
You must log in or register to reply here.
Back
Top