Multi Channel upmixing - discrete vs. matrix - AVS Forum
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post #1 of 11 Old 06-17-2014, 03:50 PM - Thread Starter
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Multi Channel upmixing - discrete vs. matrix

Hi Folks,
Help me understand this...
Say I'm watching a Blu with a 7.1 mix on it. If I'm watching on my 7.1 system with direct/dts-hd I'm getting a true discrete 7.1 mix. Great.

NOW, let's say I added front heights or front wides (or both). Do the original 7.1 speakers maintain the discrete mixes sent to them, with "matrixed" mixes sent to the new front height/front wide surrounds? Or is the whole mix (all channels) re-matrixed through all speakers and nothing is discrete?
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post #2 of 11 Old 06-17-2014, 04:06 PM
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If the new output is extracted from a pair of discrete channels, then none of them are discrete any more.

Simple example: extracting a centre output from a 2-channel CD. Sounds (e.g., vocals) that are exactly the same level and phase in the L/R speakers will phantom image at the centre of the soundstage. Those vocals can be extracted and sent to a centre speaker placed at the centre of the soundstage, where those sounds were going to image anyway.

However, that means you'll hear the vocals in triple-mono, coming from all 3 front speakers. So, it's not enough just to send those sounds to the centre speaker. The new centre signal has to be inverted and sent as an out of phase cancellation signal to the original L/R channels so you don't hear the vocals from your L/R speakers.

So 2 input channels were turned into 3 outputs. The new centre output is obviously matrix extracted, not discrete. The new L/R outputs no longer have the vocals in them, so they are no longer the same discrete channels that were on the disc, they're as matrix extracted as the centre.

Same holds true when you split a pair of channels (surrounds) into 2 pairs of outputs (sides and rears). Those new side and rear outputs are both different from the incoming discrete surround channels. Same with extracting heights and wides. The original discrete channels have information sliced out of them, so they are derived from the processing, no longer the original discrete channels.

Sanjay
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post #3 of 11 Old 06-17-2014, 05:02 PM - Thread Starter
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Quote:
Originally Posted by sdurani View Post
If the new output is extracted from a pair of discrete channels, then none of them are discrete any more.

Simple example: extracting a centre output from a 2-channel CD. Sounds (e.g., vocals) that are exactly the same level and phase in the L/R speakers will phantom image at the centre of the soundstage. Those vocals can be extracted and sent to a centre speaker placed at the centre of the soundstage, where those sounds were going to image anyway.

However, that means you'll hear the vocals in triple-mono, coming from all 3 front speakers. So, it's not enough just to send those sounds to the centre speaker. The new centre signal has to be inverted and sent as an out of phase cancellation signal to the original L/R channels so you don't hear the vocals from your L/R speakers.

So 2 input channels were turned into 3 outputs. The new centre output is obviously matrix extracted, not discrete. The new L/R outputs no longer have the vocals in them, so they are no longer the same discrete channels that were on the disc, they're as matrix extracted as the centre.

Same holds true when you split a pair of channels (surrounds) into 2 pairs of outputs (sides and rears). Those new side and rear outputs are both different from the incoming discrete surround channels. Same with extracting heights and wides. The original discrete channels have information sliced out of them, so they are derived from the processing, no longer the original discrete channels.
Awesome. Thanks for breaking that down for me!
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post #4 of 11 Old 06-17-2014, 06:18 PM
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What kind of problems does this cause? How bad?
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post #5 of 11 Old 06-18-2014, 10:56 AM
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Originally Posted by rcohen View Post
What kind of problems does this cause?


none?

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post #6 of 11 Old 06-24-2014, 07:28 AM
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How do you determine the matrix mix coefficients?
Any idea how height is extracted?
Any good articles or papers on the topic?

Thanks!
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post #7 of 11 Old 06-24-2014, 07:42 AM
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Good question. Out of curiousity,

1. Will there be a degrade in SQ if u do MATRIX?
2. If none, does it mean that a DTS HDMA 5.1 matrix to 7.1 ( using DTS NEO ) will sound the SAME to originally encoded 7.1 DTS HDMA? ( hypothecally same movie)



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post #8 of 11 Old 06-24-2014, 07:45 AM
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I'm particularly interested in how 11.1 works with matrix up mixers, like Neo:X.

It would be neat to experiment with similar techniques using JRiver.
I can do it in my pre-pro, but then I sacrifice other JRiver processing features.
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post #9 of 11 Old 06-24-2014, 08:00 AM
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Quote:
Originally Posted by rcohen View Post
I'm particularly interested in how 11.1 works with matrix up mixers, like Neo:X.

It would be neat to experiment with similar techniques using JRiver.
I can do it in my pre-pro, but then I sacrifice other JRiver processing features.
I have 7.1 heights (no back surrounds)
Neo:X, Dolby IIz (height) and Audyssey DSX all have different methods of pulling out 5.1, 7.1ch into 9.1, etc.

I prefer Neo:X - less dialogue bleed across the front stage speakers than DSX and pulls out more to the heights than IIz, which seems limited to reflective ambient sounds (mostly rain). I suppose Neo:x might affect the surrounds, but the most obvious effect is augmenting the sound out of side towers, and allowing for screen centered dialogue since the center channel is generally above or below the screen.

Last edited by flinchn; 06-24-2014 at 08:09 AM.
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post #10 of 11 Old 06-24-2014, 08:07 AM
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I really don't like DSX, since in my system it seems to make everything a muddy wash, particularly making a mess out of the bass. On the lowest setting, it makes it a little bit worse. Neo:X and Dolby IIz don't seem to have these problems, but I can't do those inside JRiver, without understanding how they do the matrix mix. I agree that Neo:X seems to cause the least problems.
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post #11 of 11 Old 07-08-2014, 08:49 PM
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When I experiment with this stuff, I find that matrix mixes that use much inverted phase can be fatiguing and strange to listen to.

I keep going back to direct 7.1 over matrix mixes, and leaving my extra channels unused. I even seem to prefer 5.1->7.1 up-mixing that duplicates the rear channels (aside from time alignment and EQ) over matrix mixes that use inverted phase.

I think I'd prefer getting a wider soundstage from spreading out the fronts, rather than matrix mixing wides with much inverted phase.
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