How Does It Know?

[herbu]

You have a 7.1 AVR with 2 of the channels "assignable" to Rear Surrounds, Front Highs or Front Wides. I know there is some 7.1 source material with the Rear Surround signals defined. But let's say you have a 5.1 source. How does the AVR decide what to send the assigned channels? How does it know a door slamming belongs in the Rear Surrounds and not the Front Highs? How does it know a plane flying overhead belongs in the Front Highs and not the Front Wides?

BTW, the title comes from an old joke. Rednecks discussing the most impressive invention of the last 100 years. They throw out planes, computers, cellphones, etc. One guy says the thermos bottle. Asked to explain, he says it keeps hot stuff hot, and cold stuff cold. But the thing he just doesn't understand is, "How do it know?".

 

[TLS Guy]

It knows, because in 5.1 and 7.1 the channels are discrete. So it is the same as stereo with with 7 tracks and one one for the LFE.

Matrix systems play tricks with phase and delays to try and figure out where things are but not well.

Atmos is different. I have not really looked at the domestic system, but the 64 channel system in cinemas, uses coordinate geometry.

You can define any point in a room with three coordinates, just like a graph defines a spot on a piece of paper with x and y coordinates.

In the 3D world you need one more coordinate to define a pint in a room say. So Dolby Atmos does not need 64 channels. It needs the track and the three coordinates to play in sink for every sound, and enough processor speed to hold it together. So the sound plus coordinates will tell which speakers to play and how loud to place that sound source accurately in the room. How much of that technology translates to the domestic version I don't know, as I have not looked into it, as I doubt in a domestic scene it will add much.

 

[herbu]

It knows, because in 5.1 and 7.1 the channels are discrete. So it is the same as stereo with with 7 tracks and one one for the LFE.

Matrix systems play tricks with phase and delays to try and figure out where things are but not well.

I understand the discrete channels. I don't understand what happens when you want to use more than the discrete channels provided in the source.

Ex: I have a 7.1 system, and play a bluray that is 5.1. My rear surrounds play something. How does the AVR decide what is appropriate to send to the rears?

Ex: I have a 7.1 system, and play a bluray that is 7.1. But instead of using rear surrounds, I have those 2 channels assigned as Front Highs. How does the AVR decide what to send the FHs?

Does a 5.1 or 7.1 source contain: L/R/C, SL/SR, RSL/RSR, FWL/FWR, FHL/FHR, and select only the channels I have configured? I don't think so. I'm guessing the AVR software uses, "tricks with phase and delays to try and figure out where things are but not well". If that's the case, are these algorithms pretty much standard and shared between all manufacturers? Does one company stand out as doing it better?

 

[TLS Guy]

I understand the discrete channels. I don't understand what happens when you want to use more than the discrete channels provided in the source.

Ex: I have a 7.1 system, and play a bluray that is 5.1. My rear surrounds play something. How does the AVR decide what is appropriate to send to the rears?

Ex: I have a 7.1 system, and play a bluray that is 7.1. But instead of using rear surrounds, I have those 2 channels assigned as Front Highs. How does the AVR decide what to send the FHs?

Does a 5.1 or 7.1 source contain: L/R/C, SL/SR, RSL/RSR, FWL/FWR, FHL/FHR, and select only the channels I have configured? I don't think so. I'm guessing the AVR software uses, "tricks with phase and delays to try and figure out where things are but not well". If that's the case, are these algorithms pretty much standard and shared between all manufacturers? Does one company stand out as doing it better?

Yes, those channels you speak of are derived. It is a matrix mathematical algorithm that analyses the channels and makes a guess were to put it based on phase and time.

 

[herbu]

It is a matrix mathematical algorithm that analyses the channels and makes a guess were to put it based on phase and time.

Thanks. That's what is interesting. Lots of discussion lately about ATMOS determining location, but I don't recall discussions about rears/highs/wides. I wonder if anyone has ever tested various brands to see if one does it better than another. I wonder if it's as good as it is going to get. It seems this is an AVR "feature" very commonly used, but given little attention... and I wonder why.

 

[TLS Guy]

Thanks. That's what is interesting. Lots of discussion lately about ATMOS determining location, but I don't recall discussions about rears/highs/wides. I wonder if anyone has ever tested various brands to see if one does it better than another. I wonder if it's as good as it is going to get. It seems this is an AVR "feature" very commonly used, but given little attention... and I wonder why.

They all use the same algorithms, and you can select the ones you want to use, at least I can. They are derived from Dolby plx, THX etc, and are just extensions of those logic algorithms.

I don't think there is a lot of interest in height channels.

In fact my rig gives good height information from 2 channel stereo with no algorithms. With good recordings of cathedral choirs, you can easily discern the organ is above the choir. Good minimal miking and speakers with a really good phase response, will confer a lot of height information and a lot else besides.