# Basic height channel question.



## hgoed (Mar 22, 2010)

I'll admit I haven't heard Prologic IIz or Audyssey DSX, but I was thinking that a single height channel might produce much the same effect. I know many people would like to put a center channel both below and above their TV, but I've read that this isn't such a good idea considering it would be the same source. A center height might be beneficial, 'though, and for me at least, it would allow much more convenient placement. Can anyone explain why all/both the implementations use stereo height? Any thoughts about making a phantom center height from these stereo channels?


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## koyaan (Mar 2, 2010)

The first I ever heard of Height channels was some years back when Telarc started issuing multichannel SACDs using the .1 channel for height rather than LFE. One of the setups that they recommended at the time was a single speaker positioned directly above the listener.lddude:


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## nholmes1 (Oct 7, 2010)

Stereo height channels would assist with directional cues, allowing for more coverage over a larger area. Honestly I am not sure if it would work well or not with a single speaker, my guess is not.


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## Joris (Apr 8, 2011)

nholmes1 said:


> Stereo height channels would assist with directional cues, allowing for more coverage over a larger area. Honestly I am not sure if it would work well or not with a single speaker, my guess is not.


Height channels will become very important in the near future worldwide. Go hor auro-3d on google (Aurophony)to read more. If you want more information, let me know.


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## hgoed (Mar 22, 2010)

I looked at the Auro site--it is basically illegible. It looks like a scanned in brochure. I didn't get much out of it other than the basic concept.


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## Mark Techer (Jan 17, 2008)

And why stop there?

I'm not sure exactly what decoders are used in a 9.1 or even 11.2 system, but stereo heights could be matrix encoded into the stereo pairs of FL and LS and RF and RS with relative ease.

I did a blog a while ago about using two 4-2-4 matrix decoders that could be used to extract two additional channels (four in total) from each side of the room - WIDE being the in-phase or "summed" signal between a stereo pair and HEIGHT being the out of phase or "difference" between a stereo pair. 

Because sounds in multi channel discrete sources do not bleed into other channels it is possible to encode these extra channels into the existing 5.1 layout. Of course to hear the extra channels from their intended locations require the additional speakers and channels of amplification as the phantoms may or may not work due to the effects of both HRTF and the shape of our ears.


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## Joris (Apr 8, 2011)

hgoed said:


> I looked at the Auro site--it is basically illegible. It looks like a scanned in brochure. I didn't get much out of it other than the basic concept.


The website is quite poor for the moment. They are working on a new version now.


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## Joris (Apr 8, 2011)

Mark Techer said:


> And why stop there?
> 
> I'm not sure exactly what decoders are used in a 9.1 or even 11.2 system, but stereo heights could be matrix encoded into the stereo pairs of FL and LS and RF and RS with relative ease.
> 
> ...


Hello Marc,

Nice to see you hear as well.
I have forwarded your blog to Wilfried Van Baelen who is the chief of Galaxy Studios and
Auro 3D. He is travalling the world around to give lectures about the system and meeting
mayor film- and recording studios. He wanted to answer you personally, and maybe he will.
At the meantime, I may tell you that the Auro 3D is a system that is not based on a matrix decoding.
The codec is on PCM level without any loss and it took more 4 years to develop it. It is now patented world-wide. It is also a system that comes with a complete solution for discrete 9.1 recording (not only in recording-studios but also on filmsets with special rigs developped for it), mixing consoles that have been modified (D-88 and DFC by Neve), mastering solutions and of course the codec that enables to output the discrete channels into existing formats such as DCP ( up to 13.1) and (audio)- BluRay. There is a lot of response to it but I am restricted by an NDA to tell you more about that. Wilfried will write you in the near future.


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## Mark Techer (Jan 17, 2008)

Joris said:


> Hello Marc,
> 
> Nice to see you hear as well.
> I have forwarded your blog to Wilfried Van Baelen who is the chief of Galaxy Studios and
> ...


I look forward to that.



> At the meantime, I may tell you that the Auro 3D is a system that is not based on a matrix decoding.
> The codec is on PCM level without any loss and it took more 4 years to develop it. It is now patented world-wide. It is also a system that comes with a complete solution for discrete 9.1 recording (not only in recording-studios but also on filmsets with special rigs developped for it), mixing consoles that have been modified (D-88 and DFC by Neve), mastering solutions and of course the codec that enables to output the discrete channels into existing formats such as DCP ( up to 13.1) and (audio)- BluRay. There is a lot of response to it but I am restricted by an NDA to tell you more about that. Wilfried will write you in the near future.


A fully discrete system would be better as whilst the WIDE channels could be full range, the HEIGHT channels I describe in my blog are band limited. Full range channels would be much better for all channels.


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## MatrixDweller (Jul 24, 2007)

Would having left/right and top/bottom speakers give more of a 3D effect to sound? 

My thinking that stereo can give you a phantom center. Add stereo top/bottom and tie the mix into the all front channels and you position the sound like on a grid (the screen being your grid).


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## ObliviusConsumr (Feb 3, 2009)

hgoed said:


> I'll admit I haven't heard Prologic IIz or Audyssey DSX, but I was thinking that a single height channel might produce much the same effect. I know many people would like to put a center channel both below and above their TV, but I've read that this isn't such a good idea considering it would be the same source. A center height might be beneficial, 'though, and for me at least, it would allow much more convenient placement. Can anyone explain why all/both the implementations use stereo height? Any thoughts about making a phantom center height from these stereo channels?


I can't speak for Audyssey on why they chose to extrapolate stereo height channels rather than a single height channel but I can tell you from my personal experience with DSX why I think they did and why I think the other posters are right. The reason is directional cues and better surround envelopment.
From what I can tell, and I may be wrong here, the height channels in my Audyssey DSX setup are extrapolated from the main channels and to a lesser degree the corresponding surrounds on the same side (left main and left surround or right main and right surround).
From my experience it really helps to tie the front and surrounds more together during pans (I like the effect and probably wouldn't buy another receiver without DSX). The same surround envelopment doesn't seem like it'd be possible with a single center height channel. 

I saw a review of some Axioms once where the reviewer used two center channels fed the same signal to create more "impact". He said it worked really well so if that's your goal you may want to try that.

On the other hand if you're a purist you might not want to do that. People often criticize the horizontal MTM setup for use as a center channel because of the off axis lobing that's caused by the same sound being produced by two different drivers hitting the listener on the end of the couch at slightly different times. So I'd guess the same would apply if you stacked two center channels vertically and the sound arrived from one earlier than the other. Essentially you might end up with muddied sound. I'd guess that this is how commercial theaters are set up though for the extra volume.


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## hgoed (Mar 22, 2010)

From what I remember, even Audyssey admits that we perceive the height information less acutely. Conceptually, I have a hard time even trying to imagine sounds above me I've been able to localize, especially within the 8-10 ft difference that stereo height information would be presented. Practically, stereo height channels would require drilling more stuff into my walls vs. being able to rig one speaker on top of my monitor. 

Regarding the top and bottom centers--if your eyes and ears are in the ideal position, centered, I don't think the lobing (?) would be much of a problem (I'm talking about our brain's processing, not some physics diagram of cancellation), but from my perspective, if one is going to add another speaker/amp/processed path, it should add information that isn't already there, otherwise you're just adding power.

Again, I'm not an expert by far, just one who's interested and hopes to stumble upon the ideal HT system before I'm effectively deaf and blind.

p.s. I'd really like to try DSX but right now the amps offering it use over 1kWH in power, so I need to wait for a software, or class D/T solution. I have a feeling I'll be waiting a while unless I can find another decent decoding solution.


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## Mark Techer (Jan 17, 2008)

MatrixDweller said:


> Would having left/right and top/bottom speakers give more of a 3D effect to sound?
> 
> My thinking that stereo can give you a phantom center. Add stereo top/bottom and tie the mix into the all front channels and you position the sound like on a grid (the screen being your grid).


When dual centres are used, you really need to be vertically centered to hear the phantom image. If your closer to either top of bottom speaker, the sound will collapse to the nearer speaker. Dual centres also add the issue of comb filtering 



ObliviusConsumr said:


> I can't speak for Audyssey on why they chose to extrapolate stereo height channels rather than a single height channel but I can tell you from my personal experience with DSX why I think they did and why I think the other posters are right. The reason is directional cues and better surround envelopment.


Exactly. It has mids and highs and is therefore directional. You don't want this effect (which should be spacious) collapsing into a single point source. 


> From what I can tell, and I may be wrong here, the height channels in my Audyssey DSX setup are extrapolated from the main channels and to a lesser degree the corresponding surrounds on the same side (left main and left surround or right main and right surround).


My understanding is the same. The original EX adapters like Circle Surround offered a height channel which was takes from the surrounds. Given height channel speakers go above the screen, you need them producing sounds related to the screen images, not the surrounds. 



> People often criticize the horizontal MTM setup for use as a center channel because of the off axis lobing that's caused by the same sound being produced by two different drivers hitting the listener on the end of the couch at slightly different times. So I'd guess the same would apply if you stacked two center channels vertically and the sound arrived from one earlier than the other. Essentially you might end up with muddied sound. I'd guess that this is how commercial theaters are set up though for the extra volume.


The effects of lobing has in actually on HFs. The MTM or D'Apploito (designed by Dr. Joseph D'Appolito in the 1970s) created a speaker that radiated symmetrically. As a bi-product, it also controls the vertical directivity minimizing early reflections off the floor and ceiling. When you lay an MTM on its side (as is often done for centre speakers), this "control" of the vertical directivity now affects the horizontal dispersion. If your using three MTMs for LCR and have the C laid on its side, you create an effect that might be called "an acoustical phase difference". 

If you can ever find the film THE NUGGET (not the best film, but the sound is cleverly mixed) there is dialogue that is panned from L through C and out through R. When seated off axis and when using an MTM on its side, the effecting changes it makes to the dialogue is actually quite significant. I guess you would also hear the same results listening to parts of FINDING NEMO and THE INCREDIBLES as they also both have occasional panned dialogue.


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## hgoed (Mar 22, 2010)

So, although this may continue the topic drift, for my center...what if I were to use two full range drivers next to each other, within about 1 cm, for the center? Would this be worse than one on the bottom and one on the top? I can place the top/bottom drivers equidistant from my ears as I'll be making a custom stand for my TV and the speakers. There is no way to do that horizontally after the room is set up for more than one viewer, but I can bring them close.

Expanding on that idea, and I don't really plan on doing this right now, what about one FR driver on each corner as well, matrixed from the LRC. It'd be pretty easy to matrix that information, but I haven't found a good way to extract height information that doesn't require me to buy an entire receiver. If I did I might consider height for both above and below ear level just to see what it was like.


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## Mark Techer (Jan 17, 2008)

hgoed said:


> So, although this may continue the topic drift, for my center...what if I were to use two full range drivers next to each other, within about 1 cm, for the center? Would this be worse than one on the bottom and one on the top?


Side by side would produce a degree of lobing, but I do think be better than two centres top and bottom of the screen. A close spaced vertical array at the bottom of the screen (or the top) would be better if you have the space.


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## hgoed (Mar 22, 2010)

I thought that was the case. Problem with vertical for me is that one of the drivers would be awfully close to the floor. I'd need to angle the front of the cabinet much more steeply. Well, that'll give me something to work on.


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## Mark Techer (Jan 17, 2008)

You could always tilt the whole speaker up so it 'aims' at the seated listening position.


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