A Word About HD Audio

Introduction
I've been reading some threads about the Xbox One's lack of audio bitstreaming. Meaning, the console doesn't simply lift the DTS-HD or TrueHD audio stream from the disc and feed it directly through HDMI. This has caused a number of people to become frustrated
and rather vocal. I wanted to take some time to explain why this is the case and the philosophy behind it. I also wanted to cover existing gaps the console has while operating under this mindset.

To be succinct, the Xbox One is a virtual AVR. It handles the things your AVR does before the AVR sends the final LPCM signal to the DAC. They are as follows, in order:

Bitstream Decoding
The first thing that has to happen is the bitstream needs to be decoded. Just like your AVR, the Xbox One decodes compressed audio codecs, whether they be lossy or lossless, to LPCM. Each audio codec has a strict specification that is followed when doing
this. In fact, because DTS-HD Master Audio and Dolby TrueHD are lossless, there is only one possible way for the console to decode either of these.

This process is strictly digital and is subject only to mathematics, not the quality of the hardware.

Channel Mixing
Now that we have LPCM, we need to look at two things:

• How many channels is this LPCM stream?
• How many channels are we outputting to?

This is where the stream gets either up-mixed or down-mixed to match the number of output channels. Of course, this step can be skipped altogether if the two are the same.

For down-mixing surround to stereo, we fold the surround channels into front-left and front-right channels. The center channel is also split and sent there. For up-mixing stereo to surround, the Xbox One simply adds blank center and surround channels.
Note that forcing this approach is a gap in functionality. More on that later.

Resampling
Just like how most AVRs have DACs that support a singe sample rate (mine are 192 kHz), the Xbox One resamples everything to 48 kHz. This, too, is a gap in functionality that will be covered later.

Effects Mixing
This step applies only to the Xbox One; most AVRs don't do this. This happens when you are watching a movie and zoom out to the dashboard. Not only is the movie's audio reduced by about 25%, but you also hear dashboard effects as you move about the UI.

Final Output
At this point, we have a final stream of LPCM to send out. In the AVR's case, this is sent to the unit's DACs. In the Xbox One's case, it's output to HDMI.

In this manner, the Xbox One is, again, a virtual AVR. But there are some things my real AVR does that this console doesn't seem to do. And we also need one additional setting.

Gap: Matrix Decoding
I use this a lot, actually. It comes in handy when something on Netflix isn't 5.1 discrete, but I still want to emulate 5.1 surround with dialogue coming out of the center channel. This is presently not possible with the Xbox One. It also makes listening
to stereo music more enjoyable.

Gap: Sample Rate Setting
Not everyone's AVR has DACs that run at 48 kHz. In fact, I don't think any such device has been on the market in years. My AVR has 192 kHz DACs. This means that when I bitstream something that's 96 kHz, that extra frequency response is preserved.

The Xbox One seemingly down-samples everything to 48 kHz, causing this extra information to be lost. As such, the desired final sample rate should be configurable.

I would also like to point out that 96 kHz and especially 192 kHz can do better jobs of expressing CDDA (44.1 kHz) than 48 kHz. But explaining this involves sampling theory.

Conclusion
The Xbox One doesn't support bitstreaming audio because it does that for you. This allows for a more pleasant experience to be achieved with background dashboard effects being mixed in.

However, there are some things the Xbox One needs to add.

:)

 

DTS reverting back to Uncompressed 7.1

There is absolutely nothing wrong about uncompressed 7.1.

DTS(Lossy) < DTS HD High Resolution Audio(Lossy) < DTS HD Master Audio(lossless) = 7.1 Uncompressed(lossless)

 

ATMOS and DTSX Support.

You can vote for better HD audio support, hopefully it is something they can update.

xbox.uservoice.com/.../6029319-proper-hd-audio-support

 

More acronyms than a government report

 

The problem is, many many of us have tens of thousands of dollars invested in our audio setup. We want the high end dedicated equipment to do all of that because we know it can do it the best. So why just simply pass us the audio untouched and let our
other gear deal with it.

The xb1s will *HAVE* to do this if it wants to compete in the UHD market.

 

Dang! Thanks for the detailed posting. I'm about to start upgrading my audio experience using a console.... TOSlink... DAC/amp... $200-300 headphones. Either Sound BlasterX g5 or the quirky named Schiit Magni 2 & Modi 2 rig.

Saving this thread.

 

That's an excellent point. This philosophy also seems to be similar with all-in-one WiFi Modem Router über box used by my ISP. Rogers Ontario. "Bridge it", is the battle cry....