Marantz SR6009 / SR7009 Dolby Atmos Network AV Receivers Preview

[nickboros]

Thanks Rob H. for such a detailed reply! I guess what I kept getting tripped up on was that I think the original Blu-Ray spec for the players is 8 audio channels (one for a subwoofer). So this is why I was confused about getting all of the extra "channels of audio" without having space in the Blu-Ray spec. It seems pretty amazing that they can give as much extra information for nearly 30 channels just using the existing 8 audio channels and some extra metadata AND that we don't need a new Blu-Ray player to do this.

 

[FirstReflection]

Thanks Rob H. for such a detailed reply! I guess what I kept getting tripped up on was that I think the original Blu-Ray spec for the players is 8 audio channels (one for a subwoofer). So this is why I was confused about getting all of the extra "channels of audio" without having space in the Blu-Ray spec. It seems pretty amazing that they can give as much extra information for nearly 30 channels just using the existing 8 audio channels and some extra metadata AND that we don't need a new Blu-Ray player to do this.

You're most welcome.


Yup, getting our heads around this new way of thinking about sound objects instead of speaker channels is tricky. But it's really important to remind ourselves that Dolby Atmos soundtracks do not add any channels to the recording. The recording on a Blu-ray disc is still either 5.1 or 7.1 channels, just like it's always been. And for download or streaming content, the recording is still 5.1 or 7.1 Dolby Digital Plus. As far as speaker channels go, nothing at all has changed. And this is why all Dolby Atmos soundtracks - whether on Blu-ray or via a download or streaming service - are completely backwards compatible with existing speaker systems. If you buy a Blu-ray with a Dolby Atmos soundtrack on it, you can play it on your standard 5.1 speaker system, no problem. If you download or stream a movie that advertises that it has a Dolby Atmos DD+ soundtrack, you can play that back on any standard 5.1 or 7.1 speaker system. You absolutely do not need a Dolby Atmos decoder or any new speakers just to play a Dolby Atmos soundtrack. Dolby Atmos soundtracks are completely backwards compatible. So go ahead and buy Blu-ray discs that advertise that they have an Atmos soundtrack! You won't hear any difference - it'll still sound exactly the same as the 5.1 or 7.1 soundtrack because it IS the 5.1 or 7.1 soundtrack.


But if and when you ever get a Dolby Atmos decoder and at least one extra pair of speakers, now you can hear some of those Atmos sound objects. That 5.1 or 7.1 TrueHD or DD+ soundtrack has some extra metadata piggybacking on its bitstream signal. And that metadata tells the Dolby Atmos decoder to take some of the sounds that are in the soundtrack and place them according to some X,Y,Z coordinates...to the best of its ability based upon which exact speakers you have told the AV Receiver or Pre/Pro are in use!


So Dolby Atmos soundtracks DO have some additional data vs. regular TrueHD and DD+ soundtracks. But there are no additional channels. ALL of the sounds are still mixed into those 5.1 or 7.1 channels. It's not as though there are any sounds "missing" if you play a Dolby Atmos soundtrack through a regular 5.1 speaker system. But if you happen to have a Dolby Atmos decoder and at least one pair of elevated speakers (Heights or Tops), then the Dolby Atmos decoder can "look" at that additional metadata that is piggybacking on the TrueHD or DD+ bitstream, and it can use that metadata to play some of the sounds in the recording with more precise X,Y,Z coordinates.

So you can think of it this way: the sound mixer still puts all of the sounds into 5.1 or 7.1 channels. But some of those sounds can be "plucked" out of those channels and positioned elsewhere in the room according to a set of X,Y,Z coordinates. In order to "pluck" any sounds and reposition them, some extra instructions are sent along with the 5.1 or 7.1 channels. If you do not have the decoder that can read those extra instructions, then nothing changes; you just hear the 5.1 or 7.1 channels as normal. But if you DO have the decoder, then it can look at those extra instructions and "pluck" those particular sounds out of the channel "bed" and reposition them according to those extra instructions. Exactly how close it can reposition those particular sounds to the X,Y,Z coordinates given in the extra instructions depends on how many extra speakers you are using and where you have placed them in your room.

 

[nickboros]

^^^^

This has been really helpful. I think I understand it better now. It is amazing to me that there is enough extra room in the existing 8 channels of the blu-ray spec, which is also restricted in terms of how much bitrate is allowed for the audio portion I am sure, to get out as much as approximately 30 channels of audio after the chip in the receiver decodes it. Really cool.

 

[FirstReflection]

^^^^

This has been really helpful. I think I understand it better now. It is amazing to me that there is enough extra room in the existing 8 channels of the blu-ray spec, which is also restricted in terms of how much bitrate is allowed for the audio portion I am sure, to get out as much as approximately 30 channels of audio after the chip in the receiver decodes it. Really cool.

Well, that's the thing: there aren't anywhere close to 30 channels of audio in the signal. There are only 6 (5.1) or 8 (7.1) channels. In commercial movie theaters, there can be 10 (9.1) channels.


But as far as channels of audio goes, that's it! There are no extra channels. There is no additional audio information. ALL of the sounds are contained within those 6, 8 - or in the case of some commercial cinema releases, 10 - audio channels.


The only additional information is some metadata. According to Dolby, that additional metadata adds somewhere around 20-30% more bits of data to the audio bitstream.


Blu-ray is capable of outputting 8 channels of completely uncompressed LPCM audio. Dolby TrueHD takes up approximately half as much space and bandwidth. So if the additional metadata for Dolby Atmos sound objects only increases a Dolby TrueHD 7.1 bitstream by an additional 30%, that's still way below the bandwidth limit.


So it isn't even close to having 34 discrete channels of audio. Every so often, there's just an instruction that only a Dolby Atmos decoder will understand that says, "Hey! There's a sound happening in the Left Front speaker right now. Take that sound and play it this many degrees farther to the Left, this many degrees farther forward, and this many degrees farther upward." It might also have some instructions about how "large" that sound object should be - small as a pin point or spread out across a large area - and it can also tell the Atmos decoder how that sound object should move in 3 dimensional space.


So plenty of instructions, but no new actual sounds, and no new channels.


The opposite approach would be something like Auro 3D audio. That IS adding additional channels. And they are just sending uncompressed PCM, so how do they handle it?


Well, Blu-ray can send out as much as 8 channels of 24-bit/ 96kHz uncompressed PCM. Auro 3D Audio takes our regular 7 speaker channels and limits them to 16-bit audio. That leaves them the remaining 8 bits of data per channel from the 24-bit limit. Auro uses those remaining 8 bits per channel to encode their extra "Height" channels.


With Auro 3D Audio, an audio mixer has to decide what sounds come out of which speakers. They can't just create sound objects with X,Y,Z coordinate data. No, with Auro 3D, the mixer has to place each sound into a particular speaker, array of speakers, or pan between particular speakers. In a full 13.1 Auro sound mix, that's a heck of a lot of extra work for the sound mixer. And you have to have the exact matching playback system in order to hear the mix the way it was intended.


So Auro 3D Audio starts to bump into the limitations of the Blu-ray format. It's a fairly clever way of getting around those limitations, but working with actual extra channels of audio really does become a challenge. Object-based audio makes so much more sense. The sound mixer doesn't have to worry about speakers. The playback system doesn't have to perfectly match the mix. And no additional channels of sound need to be included in the recording.

 

[nickboros]

The only additional information is some metadata. According to Dolby, that additional metadata adds somewhere around 20-30% more bits of data to the audio bitstream.

Blu-ray is capable of outputting 8 channels of completely uncompressed LPCM audio. Dolby TrueHD takes up approximately half as much space and bandwidth. So if the additional metadata for Dolby Atmos sound objects only increases a Dolby TrueHD 7.1 bitstream by an additional 30%, that's still way below the bandwidth limit.

So it isn't even close to having 34 discrete channels of audio. Every so often, there's just an instruction that only a Dolby Atmos decoder will understand that says, "Hey! There's a sound happening in the Left Front speaker right now. Take that sound and play it this many degrees farther to the Left, this many degrees farther forward, and this many degrees farther upward." It might also have some instructions about how "large" that sound object should be - small as a pin point or spread out across a large area - and it can also tell the Atmos decoder how that sound object should move in 3 dimensional space.

So the 20 to 30% extra data on top of the Dolby TrueHD soundtrack (taking only about 70 to 80% of the maximum allowed) will tell a Dolby Atmos chip in our receiver/processor what to do with all of our new channels regardless of whether we just use some extra Atmos ceiling speakers, or if we go all out and have 34 channels. The only limitation at this point is having a receiver/processor that can handle the extra channels and Dolby to give them the chip to decode those extra channels. Is that right?

If that is right is seems like it would give us a way of getting an equivalent mix to that of a discreetly mixed 34 channel mix (of say Auro) with much less information on the disc needed and fitting within the current Blu-Ray specs. I can't see how the soundtracks would sound any different. Now this is all way out there talking about 34 channels for the home when we likely don't need that many, but the potential is there if a receiver/processor manufacturer wanted to implement it?