Where does the decoding happen? So confused :-(

[cynical2]

I have a question that I'd appreciate some help with, but first I need to cover my setup(s) as background:

Family Room
Denon AVR-3802 7.1 - doesn't have TrueHD and HD-DTS decoding, 7.1 pre-outs
Toshiba HD-A2 HD-DVD player
DirecTV HR-700 HD DVR

Home Theater
Onkyo SR605 - has TrueHD and HD-DTS decoding, Sub pre-out only
Toshiba HD-A2 HD-DVD player
Playstation-3 for Blu-Ray
DirecTV HR-100 HD DVR


I'd like to have the option of running a separate amplifier for at least the fronts (LCR) in the Home Theater, but the Onkyo doesn't have those pre-outs. So, I thought about switching the receivers...Denon down to the basement HT, Onkyo up to the Family Room.

My question is whether I'll miss the decoding capability of the Onkyo if I replace it with the Denon. Or, is the decoding done in the Toshiba HD-A2 and PS-3 (I assume the DirecTV DVR never uses the encoding I'm concerned about), therefore meaning that the on-board decoding of the Onkyo isn't used?

One other thing to note: The Denon doesn't have HDMI inputs, so I would need to send the audio from the Toshiba HD-A2 and PS-3 via optical. I have no idea if HDMI audio vs optical audio makes any difference.

Please let me know how the decoding works (i.e. where it's done), if losing it would be an issue, and if there are any other potential features I may miss (that I haven't thought about). Thanks in advance for any help. It's very much appreciated.

[thxgoon]

The audio processing for the True HD and HDDTS are being done internally in your Onkyo in your current setup. These formats are only authorized to be sent via HDMI. There are no 7 channel analog outs on the A2 so your only option would be to hook it up to the Denon using digital optical. In this case, the player will convert the TrueHD stream into standard DTS of the highest bitrate and send it to the Denon. Thus you would still get great sound quality but it would be limited by DTS. What you would end up with is state of the art DTS sound and would likely lose some of the dynamics. I don't own any HD equipment so I can't vouch for hearing any difference myself. DTS is quite good and the codec allows for virtually unlimited headroom so the difference may be negligible. Maybe before going through all the trouble of switching out receivers try hooking up the optical cable to your Onkyo and see what kinds of differences you hear and if they are acceptable. Can't comment for the PS3.

Why are you looking for a new amp?

[cynical2]

thxgoon wrote:

The audio processing for the True HD and HDDTS are being done internally in your Onkyo in your current setup. These formats are only authorized to be sent via HDMI. There are no 7 channel analog outs on the A2 so your only option would be to hook it up to the Denon using digital optical. In this case, the player will convert the TrueHD stream into standard DTS of the highest bitrate and send it to the Denon. Thus you would still get great sound quality but it would be limited by DTS. What you would end up with is state of the art DTS sound and would likely lose some of the dynamics. I don't own any HD equipment so I can't vouch for hearing any difference myself. DTS is quite good and the codec allows for virtually unlimited headroom so the difference may be negligible. Maybe before going through all the trouble of switching out receivers try hooking up the optical cable to your Onkyo and see what kinds of differences you hear and if they are acceptable. Can't comment for the PS3.

Why are you looking for a new amp?

Thanks, thxgoon. Unfortunately, I'm an idiot and don't follow some of what you said. Would I still get 7-channel output (correctly decoded) over optical in the scenario you describe? Or, would it use only 5 channels, or not send the intended signal to each of the 4 surrounds, or...??

The suggestion you make on trying optical on the Onkyo is a good one, and something I could try. It seems like to really test this out then I need either a TrueHD or HD-DTS encoded DVD. Is there a "master list" somewhere of movies encoded that way? Quite frankly, I have no idea if I own any that are encoded that way or not.

My concern is that (I assume) Blu-ray discs will be encoded that way more-and-more in the future, so I don't want to make a change I'll regret (i.e. not be able to use the full 7 channels as intended with the latest HD encoding). Am I making sense, or way off base?

My reasoning for wanting the option of an amp is that I tried some relatively inefficient speakers in my HT and the Onkyo just couldn't push them as loud as I wanted to go. I've thought about just upgrading to the SR805, which would give me about 40% more power plus the option to add an amp later if need be (has 7.1 pre-outs, unlike my SR605). But, if it's as simple as moving my Denon to the HT, and I can avoid replacing the receiver, then that would be a much better (cheaper) option.

[thxgoon]

cynical2 wrote:

Or, would it use only 5 channels, or not send the intended signal to each of the 4 surrounds, or...??

Actually I don't know. I wish I owned an HD player of some sort as I'd probably know a lot more about them. Maybe someone else will chime in. Here is a link I found from Dolby's website. It seems that they package a core 5.1 audio stream in the TrueHD stream for playback on legacy recievers. So, if you end up getting Dolby D out of the optical connection it looks like you'll belimited to 5.1 but I thought I read somewhere that the A2 acutally re-mixes the audio in DTS, and in this case I *think* it will be 7.1.

What is the price difference for the 805? Considering that you'll lose HDMI switching, TrueHD, DTSHD and video up conversion from other equipment (does the onkyo have Audessey?) it might be worth the difference. Should you plop the Denon in the system you may well end up spending more on switchers and time banging you head against the wall trying to get HDMI and optical from the PS3 at the same time. (read a thread where this was a problem. Dunno if it was ever resolved). On the flip side, the 3802 is a great amp and could possibly power your new speakers and you won't have to buy an amp. Too many possibilities!! I'd start by experimenting with your Onkyo using legacy connections and see how things turn out. Chances are with the old connections it will behave just like your 3802.

[bobgpsr]

The older digital audio format carried over coax or optical Toslink is called S/PDIF. Your Denon has that. But S/PDIF is only allowed to carry two channel linear PCM or lossy 5.1 (legacy DD or legacy DTS) as a matter of policy. The HD-A2 will decode, mix with commentary audio, and then re-encode to lossy legacy 1.5 Mbps DTS for output on optical Toslink for any HD DVD it plays. The quality of 1.5 Mbps DTS is very good but not up to the theoretical quality of a true lossless format.

Your Denon ought to be able to take the 5.1 DTS optical input and apply DD PLIIx to it in order to drive the back surrounds for 7.1 sound (this may have to be a manual forcing step -- see your AVR manual).

[hddummy]

To answer your original question... The HD-A2 and PS3 both do decoding for HD codecs on board. They send PCM over HDMI only and do not send bitstream to your receiver for HD codecs. Your Directv does not support HD codecs and is probably sending bitstream dolby digital. If you don't use HDMI for your HD-A2 and PS3 you will not get 7.1 discrete channels and will rely on your receiver to mix the rear surround channels from the 5.1 signal.

Is using component/SPDIF bad compared to HDMI....I don't think so, but that is really up to you to decide.

[thxgoon]

Edit: Found this DTS website that seems to sum it up pretty well.

[cynical2]

Thanks Bob, Matt, and thx! Very helpful, and I will read the link that thxgoon posted.

I've been travelling all day (now in Livermore, CA), so I have lots of reading to do tonight.

Thanks again!