Problem with the 7.1 analog inputs on my Yamaha HTR-5790 is that there is no way to make them do any processing, they only go straight through. Therefore, I am stuck with whatever functions my Oppo BDP-95 has, and those are limited to volume, delay, and mixdown. The Oppo offers no functions to convert 5.1 to 7.1 using Dolby Pro Logic II x, for example. With an AC3 connection, I should be able to select whatever processing I like, but then I have a compressed signal, and therefore am losing the full resolution of DVD-Audio and SACD recordings. I can see why the receiver is like this, it must only have 2 ADC's inside, and it would need 6 or 8 to handle processing of analog multichannel inputs. Are there any receivers that DO handle such processing???
This makes one of the fundamental issues in Surround, the inherent incompatibility of 5.1 and 7.1, much worse. To explain, requires a history lesson.
I was becoming an audiophile just as the original Quadraphonic wars were running. Despite their differences in implementation, all Quadraphonic systems simply assumed a 4 channel speaker layout, 2 speakers in front, and 2 in back as mirror image.
It turns out that this 4 speaker configuration is fairly worthless. Humans do not have very good front-to-back auditory sensitivity. Things in back are somewhat muted, but it's hard to have any idea of where they are unless you turn your head.
When this was all re-thought for Home Theater, it was fundamentally changed. Instead of Quadraphonic (because more is better or something) we got Surround, in which an ambient soundfield is created arournd the listener, starting with SIDE speakers. This actually has some perceptual utility, maybe (though I think that often multichannel listeners don't appreciate the forward depth of stereo systems, which is often superior to multichannel in practice for various reasons, one of them being the confounding effects of the center channel, which IMO should be eliminated).
But somehow, the sense that "back" was needed still seemed important to some people. So, the 5.1 specification fudges the side speaker position so that they are also somewhat behind the listener. Often the specification is something like 90 degrees to 110 degrees, but most people, especially the relatively uniformed, put their side surrounds much further back that 110 degrees.
When you get to 7.1, finally it is done correctly, with both sides and back speakers. But now, the sides are supposed to be at 90 degrees, as close as possible, right on the sides of the listener.
So if you set up your system for 7.1, as I have finally done in my kitchen system (sans center channel, which is being automatically added back into the front stereo pair), it will not play 5.1 recordings, which are the vast majority, in the way that most 5.1 systems will play them. There is no back signal at all.
Effectively you need some kind of processing like Dolby Pro Logic II x (which, btw, my Yamaha receiver has, it says so right on the front, but it is ONLY applied to digital inputs). Although Dolby Pro Logic is mostly known for generating fake surround from stereo, it also features a matrix for converting 5.1 to 7.1. Although you could simply duplicate the side signals in the backs, and some schemes actually do that, it's best handled through a matrix. What I've heard described in a matrix where the sameness between the sides is subtracted from the backs. It might also benefit from some kind of steering which leaves things alone if they appear to be concentrated in one speaker.
Now that we have endless named proprietary schemes for doing matrixing we don't have any plain vanilla matrix boxes to fool around with as in the good old days. Stuck with the fact I can't actually use the Pro Logic II x on my Yamaha, or find a simple 5.1 to 7.1 outboard converter I could stick in between my Oppo and Yamaha, I now dream of building such matrix boxes myself.
Update: I may already have the answer to this problem in an unexpected place.
Two years ago I started buying Integra Research RDC-7 surround preamps simply as stereo DACs because they have dual differential 1704's, something I was pursuing at the time. For various reasons, I decided not to use this unit, and the low 1.0V voltage for I/O would be problematic in my high end living room stereo. I had reached the point where I was thinking of recycling at least one of these beasts (the beat up looking one) and possibly both because of no perceived need.
Sadly, the manual for the RDC-7 is not actually available, what one finds online is the RDC-7.1, a different beast.
Reading the manual for the RDC-7.1 it is clear that Dolby Pro Logic II x can be applied to the multichannel input (it lists the various options for multichannel inputs, and that is one of them).
I suspect either this or something similar is available on my RDC-7, especially because it has an "Upgraded" tag on the front. It appears the THX Ultra 2 has a "Cinema" mode which also expands 5.1 to 7.1 surround. In any case, this $4500 surround controller is not limited to "straight through" or "pure" for the multichannel inputs as the Yamaha HTR-5790 is. Perhaps that's the deal, to do the cool stuff you need to get the actual preamp/controller.
Since the time this was made and now, generally all Home Theater Receivers and Surround Processors have been eliminating analog multichannel inputs, which I think is a bad idea. In addition the the compressed AC3 "Dolby Digital" signal, newer products transfer multichannel through HDMI, or at least HDMI connectors. This may have the advantage that a digital signal is being transferred, and a layer of DAC and ADC may therefore be avoided. I think that issue is extremely overrated--surprisingly digital coversion, especially to 24/96 and above, is essentially lossless and about as good as a pure analog interface--the kind high end audio has been built upon from the beginning. Plus, analog signals do not have complex clocking issues or cause RFI from high speed pulses. I am also not sure you will always get a full resolution signal via HDMI from all kinds of discs. I have heard HDMI clocking may be problematic (but Oppo fixed this in the BDP-205) also.
However, if it turns out I can't use the Integra Research to do my 5.1 to 7.1 expansion, any HTR with HDMI multichannel inputs and Dolby Pro Logic II x (or perhaps THX Ultra 2) will do.
I will first see if my RDC-7 *can* convert 5.1 to 7.1 through the multichannel inputs, and if so, begin working on incorporating it into my kitchen system. My Yamaha HTR would then do nicely as a multichannel amplifier, possibly supplemented by a high end stereo amp for the front channels.
Addendum: Chesky put forward an alternative use for 6 channels in which the back surrounds are removed (they aren't THAT big a deal anyway) and replaced with front speakers at the widest possible positioning. (Stereo can't use the widest positioning because that would destroy the phantom center image.) Yahama and others used the extra two channels as "Presence" speakers which are above the stereo speakers. I didn't mean to necessarily disparage these ideas, I have just found it more convenient as well as more typical and supported to have surround back speakers.
Dolby Pro Logic II x is not the only process to convert 5.1 to 7.1. I already made that clear, but in the minds of many, all that older stuff has now been replaced by Dolby Atmos. I think thats way over the top for home theater, and particularly for 5.1 to 7.1 conversion. I would stay away from any process that has mandatory automatic room correction, though I'm not sure Atomos actually mandates that.
By all acounts (though none might be informed) the 5.1 to 7.1 conversion in Dolby Pro Logic II x is a matrix applied to the surrounds ONLY. It does not reference the front or center speakers. So, in principle, you could do this or a similar conversion with two inputs and three outputs. This is a relatively simple thing, and for a 7.1 system, perhaps just what is needed. As I said, Atomos looks way over the top.
In addition to "surround" formats, there are also some special formats like Amiphonics and Ambisonics. These may require stereo back speakers to work. These formats are somewhat controversial and I still wonder how well they actually work. However, I purchased a few recordings of this kind, and that is another use for back speakers. In this case, replugging connections may be the best way of handling it, plugging the 5.1 surround outputs into the back.
This makes one of the fundamental issues in Surround, the inherent incompatibility of 5.1 and 7.1, much worse. To explain, requires a history lesson.
I was becoming an audiophile just as the original Quadraphonic wars were running. Despite their differences in implementation, all Quadraphonic systems simply assumed a 4 channel speaker layout, 2 speakers in front, and 2 in back as mirror image.
It turns out that this 4 speaker configuration is fairly worthless. Humans do not have very good front-to-back auditory sensitivity. Things in back are somewhat muted, but it's hard to have any idea of where they are unless you turn your head.
When this was all re-thought for Home Theater, it was fundamentally changed. Instead of Quadraphonic (because more is better or something) we got Surround, in which an ambient soundfield is created arournd the listener, starting with SIDE speakers. This actually has some perceptual utility, maybe (though I think that often multichannel listeners don't appreciate the forward depth of stereo systems, which is often superior to multichannel in practice for various reasons, one of them being the confounding effects of the center channel, which IMO should be eliminated).
But somehow, the sense that "back" was needed still seemed important to some people. So, the 5.1 specification fudges the side speaker position so that they are also somewhat behind the listener. Often the specification is something like 90 degrees to 110 degrees, but most people, especially the relatively uniformed, put their side surrounds much further back that 110 degrees.
When you get to 7.1, finally it is done correctly, with both sides and back speakers. But now, the sides are supposed to be at 90 degrees, as close as possible, right on the sides of the listener.
So if you set up your system for 7.1, as I have finally done in my kitchen system (sans center channel, which is being automatically added back into the front stereo pair), it will not play 5.1 recordings, which are the vast majority, in the way that most 5.1 systems will play them. There is no back signal at all.
Effectively you need some kind of processing like Dolby Pro Logic II x (which, btw, my Yamaha receiver has, it says so right on the front, but it is ONLY applied to digital inputs). Although Dolby Pro Logic is mostly known for generating fake surround from stereo, it also features a matrix for converting 5.1 to 7.1. Although you could simply duplicate the side signals in the backs, and some schemes actually do that, it's best handled through a matrix. What I've heard described in a matrix where the sameness between the sides is subtracted from the backs. It might also benefit from some kind of steering which leaves things alone if they appear to be concentrated in one speaker.
Now that we have endless named proprietary schemes for doing matrixing we don't have any plain vanilla matrix boxes to fool around with as in the good old days. Stuck with the fact I can't actually use the Pro Logic II x on my Yamaha, or find a simple 5.1 to 7.1 outboard converter I could stick in between my Oppo and Yamaha, I now dream of building such matrix boxes myself.
Update: I may already have the answer to this problem in an unexpected place.
Two years ago I started buying Integra Research RDC-7 surround preamps simply as stereo DACs because they have dual differential 1704's, something I was pursuing at the time. For various reasons, I decided not to use this unit, and the low 1.0V voltage for I/O would be problematic in my high end living room stereo. I had reached the point where I was thinking of recycling at least one of these beasts (the beat up looking one) and possibly both because of no perceived need.
Sadly, the manual for the RDC-7 is not actually available, what one finds online is the RDC-7.1, a different beast.
Reading the manual for the RDC-7.1 it is clear that Dolby Pro Logic II x can be applied to the multichannel input (it lists the various options for multichannel inputs, and that is one of them).
I suspect either this or something similar is available on my RDC-7, especially because it has an "Upgraded" tag on the front. It appears the THX Ultra 2 has a "Cinema" mode which also expands 5.1 to 7.1 surround. In any case, this $4500 surround controller is not limited to "straight through" or "pure" for the multichannel inputs as the Yamaha HTR-5790 is. Perhaps that's the deal, to do the cool stuff you need to get the actual preamp/controller.
Since the time this was made and now, generally all Home Theater Receivers and Surround Processors have been eliminating analog multichannel inputs, which I think is a bad idea. In addition the the compressed AC3 "Dolby Digital" signal, newer products transfer multichannel through HDMI, or at least HDMI connectors. This may have the advantage that a digital signal is being transferred, and a layer of DAC and ADC may therefore be avoided. I think that issue is extremely overrated--surprisingly digital coversion, especially to 24/96 and above, is essentially lossless and about as good as a pure analog interface--the kind high end audio has been built upon from the beginning. Plus, analog signals do not have complex clocking issues or cause RFI from high speed pulses. I am also not sure you will always get a full resolution signal via HDMI from all kinds of discs. I have heard HDMI clocking may be problematic (but Oppo fixed this in the BDP-205) also.
However, if it turns out I can't use the Integra Research to do my 5.1 to 7.1 expansion, any HTR with HDMI multichannel inputs and Dolby Pro Logic II x (or perhaps THX Ultra 2) will do.
I will first see if my RDC-7 *can* convert 5.1 to 7.1 through the multichannel inputs, and if so, begin working on incorporating it into my kitchen system. My Yamaha HTR would then do nicely as a multichannel amplifier, possibly supplemented by a high end stereo amp for the front channels.
Addendum: Chesky put forward an alternative use for 6 channels in which the back surrounds are removed (they aren't THAT big a deal anyway) and replaced with front speakers at the widest possible positioning. (Stereo can't use the widest positioning because that would destroy the phantom center image.) Yahama and others used the extra two channels as "Presence" speakers which are above the stereo speakers. I didn't mean to necessarily disparage these ideas, I have just found it more convenient as well as more typical and supported to have surround back speakers.
Dolby Pro Logic II x is not the only process to convert 5.1 to 7.1. I already made that clear, but in the minds of many, all that older stuff has now been replaced by Dolby Atmos. I think thats way over the top for home theater, and particularly for 5.1 to 7.1 conversion. I would stay away from any process that has mandatory automatic room correction, though I'm not sure Atomos actually mandates that.
By all acounts (though none might be informed) the 5.1 to 7.1 conversion in Dolby Pro Logic II x is a matrix applied to the surrounds ONLY. It does not reference the front or center speakers. So, in principle, you could do this or a similar conversion with two inputs and three outputs. This is a relatively simple thing, and for a 7.1 system, perhaps just what is needed. As I said, Atomos looks way over the top.
In addition to "surround" formats, there are also some special formats like Amiphonics and Ambisonics. These may require stereo back speakers to work. These formats are somewhat controversial and I still wonder how well they actually work. However, I purchased a few recordings of this kind, and that is another use for back speakers. In this case, replugging connections may be the best way of handling it, plugging the 5.1 surround outputs into the back.
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