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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56416

  • alphaSquared
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I have an area of my loft dedicated to a modest home theater.
LG OLED TV with an Apple TV streaming to it (no other source inputs).
Currently looks like the attached photo.

 

I only use this setup for TV & films.  I've got a computer audio setup driving DMLs for serious music elsewhere in the loft.

Goal --->  Being able to properly actually hear center channel information.

Current plan:
-- Hang the TV on the bookcase.
-- Get rid of the old sound bar.
-- Replace the left and right speakers with DML panels hanging from the book case.
-- Use a DML based solution for center channel reproduction.
-- Move the console on which the TV currently sits.
Note: No plans for rear (surround sound) speakers.  They don't work in the space or for the way we otherwise use the space.

DML's for the center channel provide some interesting options:

-- A single DML panel hanging somewhere;
-- Two DML panels next to the the Left & Right DML panels in the configuration that Magnepan has explored to create a "virtual" or "phantom" center channel; or
-- Adding a center channel reproducing exciters to the planned left and right channel DML panels (DMLs have strange and wonderful properties).

What I need

Regardless of the physical DML implementation I still need to (and maybe not in this order):

-- get, extract, or synthesize a digital center channel signal,
-- optimize/craft that signal (with DSP),
-- convert the signal to analog, and
-- amplify it.

An AV receiver or separates will have me paying for a bunch of functionality and connectivity I don't need and do so at the expense of poorer quality amplification, DSP, etc than I think (hope) I can configure with a miniDSP solution.

Output optical from the TV to an SHD Power gives me DSP, DIRAC, and more than enough quality amplification to drive the left and right channels.
(Of note: the DML exciters don't really need a lot of amplifier power (50W into 8 Ohms more than adequate).

Questions

-- How do I apply DSP to and amplify the center channel DML panel(s)?
-- Could I use the RCA subwoofer outputs to external amplifiers driving the center channel DML panel(s)?
-- If I use the RCA outputs can I apply DSP to achieve something close to a center channel signal?
-- What about using an SHD or SHD Studio for the signal processing then out putting the left - center - right signals to external amplifiers?

I have come across some ideas to simulate surround and center channel reproduction:

 -- ...set up my own matrix surround sound system
--  Build a passive matrix speaker network which decodes surround sound
--  Matrix Decoder (Wiki)

​​​​​​​Some of these "ideas" go back to the 1990s, but I wondered if they might help guide me/us to a workable solution.

Any help appreciated.
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Last edit: by alphaSquared. Reason: accidentally submitted the post before completing it.

SHD for home theater L-C-R channels? 1 month 2 weeks ago #56417

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Could I do what I want more simply than I thought?

The DDRC-24 User Manual shows the following diagram:



Given this, it seems like it should additionally enable me to do the following:



Then use the DSP try things like:

1.  Send stereo voice range frequency information to the respective center channels.
2.  Send mono voice range frequency information to each center channel.

Wouldn't either of the above give me something approximating a phantom/virtual center channel along the lines of what Magnepan has tried?
Not necessarily extracting a dedicated center channel signal, but could this work?

I guess this leads to other questions, like:

- Would the DDRC-24 enable me to easily/conveniently control volume of the DML speaker panels?
- Anything else I have missed in thinking about this?

Guidance appreciated.
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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56418

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As this is intended to be a home theatre setup my  main thought on reading your post is that you made no mention of a subwoofer?

Honestly I think what you really want is an AV amp to downmix to whatever mix of channels you actually want, which really should include the subwoofer channel if you want proper movie audio. 

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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56419

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Given this, it seems like it should additionally enable me to do the following:



Then use the DSP try things like:

1.  Send stereo voice range frequency information to the respective center channels.
2.  Send mono voice range frequency information to each center channel.

Wouldn't either of the above give me something approximating a phantom/virtual center channel along the lines of what Magnepan has tried?
Not necessarily extracting a dedicated center channel signal, but could this work?

I'm not totally clear what you are trying to describe here. Are your two input channels to the the miniDSP the left and right channels of a stereo downmix from your TV? If yes then you could send the sum of these to a center speaker if you really wanted but I'm not clear what the two signal you have in mind going to apparently two center speakers are. However, none of this will replicate a true movie center/dialogue channel so it seems like a lot of effort to not do something as well as an AV amp wouuld.

For movies I run my own system in a 2.1 configuration, using an OPPO blu-ray player to give me a stereo downmix of the main channels whilst keeping the LFE channel to my subwfoofer. It works pretty well but if I were to want to improve on it I'd want to take advantage of proper center and surround channels.

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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56420

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Hi UItrasonic -- The DMLs I've developed have sufficient low end for my current needs.  No subwoofer needed for this specific application.

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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56421

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Ultrasonic,

Magnepan played around with this idea... see: www.magnepan.com/model_MC1

"No place for a center channel speaker?

The photo below is of a demonstration in a hotel during a Consumer Electronic Show. The MC1s immediately flanking the on-wall video monitor provide a dual center channel array which can outperform a single center channel speaker.
A pair of our on-wall speakers achieves a center channel image in the same manner as a stereo system achieves a center image. By angling the speakers approximately 30 degrees to the wall, the center channel speaker on the left of the video monitor is on-axis with the viewer off to the right--- and consequently is louder than the center channel speaker on the right of the monitor (which is closer to the viewer). This "pulls" the audio image to the left and keeps the dialog centered on the screen better than point source speakers. It also raises the center channel image to the same height as the screen.
Finally, when the Magneplanar on-wall speaker is used with a flexible bass management system, a large, full-range Magneplanar sound in the middle can be achieved with our on-wall design. Once you have heard this concept, you won't be tempted to buy one of those sleek center channel speakers designed for flat panel video monitors.
And there is a bonus for those willing to install this unorthodox concept. In blind-fold testing, listeners found that center channel dialog and information was easier to understand with a "Maggie" dual center than with a conventional single center channel speaker. Extensive research on speech intelligibility is available on the internet.
A word of caution-- Happy customers are our best means of advertising (word-of-mouth). If you are considering MC 1s, they will sound much better if kept away from corners-- especially for front channel applications. Speakers never sound best in corners and if you need help, please feel free to call us for specific advice.
If you have the option, side-wall placement of the MC 1s will give the best performance in a shoe-box shaped room. Place the speakers on the side-wall, about 4 to 6 feet from the front wall."
  

I have very limited goals for this build.  My DML panels give me great left and right channel sound.  
Their clarity, lead me to make the conjecture that sending some version of center channel information to center dedicated DMLs will give me the quality and clarity of dialog I don't currently have.
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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56426

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I tried to clarify about but I think you may have missed my question. Exactly what processed signal do you want to be able to send to the center speakers? 

I'm not sure any miniDSP will be able to do exactly what you'd like but the answer to the above will be important to know to be sure. I'm fairly sure Dirac Live will be of no use to you. A 2x4 HD wouuld allow you to send a sum of left and right channels to the center speakers but I don't think this is what you really want, and I don't think it would sound great.

An AV amp/processor to provide true center channel info still seems the best idea to me, and I'd be surprised if this isn't what was used for the demo you mentioned above.

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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56429

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Ultrasonic,

The sum of left and right channels to the center speakers, with a roll off of below voice frequencies would work for me.
Remember, I don't really have an interest (with the described build) to deliver a movie theater experience.
I want to emphasize voice (think rapid dialog in an Aaron Sorkin TV show or film) in a center channel.

I appreciate that an AV amp/processor could deliver me "true center channel".  
The issues being:

-  I don't need the complexity of such systems as I have a single streaming input.
-  I prefer selecting my own amplifiers (typically Hypex NCore or IcePower).  They work wonderfully with my DMLs.

To get the same quality amplification takes one to AV separates with the entry level at Emotive - great gear, just way more functionality and cost than I think I need to spend.

If miniDSP had a plugin for one of their DSPs that decoded "true" center channel, I'd have an elegant solution.
Alas, unless someone has a very clever solution, I need a synthetic center channel solution.

Maybe your thought of a 2X4 HD gets me what I need.

Much appreciated.

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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56431

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On the AV amp front the middle ground option would be to get an AV amp/processor with pre-amp outputs to then connect to your chosen amps.

You may have thought these through but I can see two key issues with what you are proposing:
  1. An issue with sending the sum of left and right channel to the center speaker is that effects that are intended to be panned to the left or right will now also be coming from the center. I suppose the result will be to significantly narrow the apparent soundstage, as if your left and right speakers were about mid-way between their true position and the center.
  2. For a central listening position it will be possible to ensure time-alignment of the left, right and center channels so that they sum together properly. For any other seating positions this will not be the case and the sound quality will be degraded. A key reason that a center speaker is used in home cinema setups is to avoid this issue. 

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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56432

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re:

You may have thought these through but I can see two key issues with what you are proposing:

  1. An issue with sending the sum of left and right channel to the center speaker is that effects that are intended to be panned to the left or right will now also be coming from the center. I suppose the result will be to significantly narrow the apparent soundstage, as if your left and right speakers were about mid-way between their true position and the center.

I do recognize that I'll likely lose some center channel "effects".  That said your comment does give me an idea... as DMLs give me the ability to separate the left & right speakers very far apart and still have an extraordinary sound stage I think a wide DML placement might offset some of the narrowing of the stage you anticipate.  Easy to move things around.

Another reason this doesn't worry me too much... many films - even from not long ago - have just re-mastered their sound with synthetic/contrived center channel information that doesn't do much more than what I have suggested doing.  Most independent films record in stereo and then create a center channel afterwords.  
Interestingly, even now (with just stereo sound) watching talking heads on news programs I hear all dialog perfectly fine.  I'd wager they record in stereo too.  

I will miss panning in big action block buster films, but it won't diminish the quality of my life/experience all that much and gives me an excuse to go to an actual movie theater ;-)

2.  For a central listening position it will be possible to ensure time-alignment of the left, right and center channels so that they sum together properly. For any other seating positions this will not be the case and the sound quality will be degraded. A key reason that a center speaker is used in home cinema setups is to avoid this issue. 

Noted and appreciated.  Kids emancipated themselves a few years back.  Just me and my wife cuddled up on the center seat.  If the kids do come home for a visit we don't want them to get too comfortable.  Love them.  Don't want to live them anymore.

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SHD for home theater L-C-R channels? 1 month 2 weeks ago #56435

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  1. An issue with sending the sum of left and right channel to the center speaker is that effects that are intended to be panned to the left or right will now also be coming from the center. I suppose the result will be to significantly narrow the apparent soundstage, as if your left and right speakers were about mid-way between their true position and the center.

Thinking about it I realise I overstated the point in bold, since once you've adjusted the summed center channel volume to match the left and right you'll essentially be using an average of the left and right, which will reduce the amplitude of signals panned to one side.

My own movie watching is generally just at the central position where personally I find my main hifi more than capable of giving clear central dialogue. 

If you're set on experimenting though I do think that a 2x4 HD is probably the most sensible option to go with. The DAC performance of an SHD is better but you'd be paying a lot extra for this, in large part for features that you wouldn't use. You could at the very least use a 2x4 HD to try this out and decide if it is really worth it or not.
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SHD for home theater L-C-R channels? 1 month 1 week ago #56504

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Response from miniDSP DevTeam

Thanks for your interest in our products.
That's a neat setup to do 

The SHD is indeed a powerful platform that would do stereo in, but it wouldn't "decode" the L/R/C from your optical bitstream Dolby/DTS signal. Only AVR/AVP with a dolby/DTS license would do such thing. 

The SHD would however be able to take L&R (from the optical) and expand it to L, R, Center (with the signal mixer for center). It would be a simulated center channel for that case. Here is an example matrix. 

https://attachment.freshdesk.com/inline/attachment?token=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpZCI6NDcwODkzNDI5MzAsImRvbWFpbiI6Im1pbmlkc3BoZWxwLmZyZXNoZGVzay5jb20iLCJhY2NvdW50X2lkIjoxMjM0MDUyfQ.F0z994WziCkrngOgkFphJiVhrAtY_Yl4RyTz8CYw1Q4

Hoping this info helps and feel free to contact us if you have further questions. 

Best Regards
miniDSP DevTeam

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