Axiom Home Page Forums General Discussion Home Theater Another Reason to Run Multi-channel

Multi-channel is great for surround-sound and effects but here's another reason to run it instead of stereo when listening to music.

My room response for two configurations is shown below. The blue trace is 2.1 channel stereo with a 40Hz receiver cut-off. The red trace is 7.1 channel stereo with an 80Hz receiver cut-off. The 80Hz cut-off removes the dips at 75Hz & 90Hz shown on the red trace. The multi-channel configuration almost eliminates the comb-filtering (the dips that occur every 25Hz or so on the red trace) that results from the wall that is 11 feet behind my listening position (see my room below).

BTW, my bottom-of-the-line Denon is putting out less than a watt per channel to achieve these SPLs.

Mo, you used the term "7.1 channel stereo"; did you mean that literally, i.e. just duplicating each main in the surrounds on that side, or were you referring to surround processing such as DPLIIx to extract ambience and send it to the surrounds?

Hi John,

In the case of the graph I posted above, I had my Denon set to 7-channel stereo (plus my sub).

Denon defines 7-channel stereo as follows:

The front left signal is output to the surround and surround back left channels. The front right signal is output to the surround and surround back right channels. The in-phase component of the left and right is output to the center. Use this mode to enjoy stereo sound.

My Denon also supports DD, PL, PLII, DTS, DTS-ES, DTS Neo:6, DTS 96/24. Some of these formats also support something called movie or music mode. When I listen to 2-channel recordings, I can engage 7-channel stereo, PLII or Neo:6. The receiver also gives me the ability to control various parameters for these modes like image, panorama, dimension, center width. I can't really decide which format I like the best with 2-channel recordings.

Your question was timely because I don't understand the difference between 7-channel stereo, PLII and Neo:6. What is meant by "extracting the ambience" for example? What's the mathematical definition of ambience? And mathematically, what is different between 7-channel stereo, PLII and Neo:6?

What's really comical is that when I bought this receiver two years ago for 350 Canadian bucks, I was really in the market for stereo only. And I couldn't find a stereo only amp so I bought this one. After I unpacked it and realized what I bought, I spent $50 on a used, no name centre and Sony rears and all of a sudden, I had me a "home theater" . I already had a DVD player that had DTS and DD capability and I didn't even know it .

Now that I've spent a ton of cash on my home theater, I feel a need to find out as much about these formats as possible.

Okay, that is then just the all stereo option that duplicates the same sound in each side(and both mixed to the center speaker). It isn't surprising that the smoothness of the room response would be improved by having the same sound in multiple speakers, but that generally isn't viewed as the best mode for typical use. It's often said to be well-suited for parties, etc., where a more uniform sound is wanted for many people in a room, but it isn't really natural-sounding to have exactly the same sound as is coming from the front also coming from the side and back speakers.

The difference between that and DPLII(or x), which I use most commonly for any type of two-channel material, is that the DPLII processing detects the phase differences in the reflected sound which has been mixed into the two front channels(there was no place else to put it) although it originally came from directions other than the front at the actual performance. It then extracts the out-of-phase material which represents reflections that came from the sides and back and steers it to the surrounds where it belongs. The result is a little closer to the live listening experience.

I hope she has ear plugs in, those freq's can get to you after some time...

Neo:6 proceeds on the same general basis(as does Logic 7 on HK receivers), but the implementation of course differs a little between the various manufacturers. Neo:6 expands to as many as 6(surprise)separate channels, while DPLIIx and Logic 7 can do(you guessed it)as many as 7. The DPLIIx implementation also has adjustments to change the center width between the mains and center speaker and the "dimension" representing the relative amount of material(not simply a volume adjustment)which is sent from the front channels to the surrounds.

In my setup, I generally prefer the Neo6 decoding. I've never been impressed at all by Logic7, and DPLII, at least on my H/K seems to strip out the high frequencies.

I've been playing around with the surround settings for music, and have found that DPLII seems to do the best at expanding the soundstage without smearing the imaging too much. I haven't gone through all the changes to center width, panorama and all that with Neo6, but it seems to make instrument placement a little too diffuse for me.

If you guys have Circle Suround, try that. It does an amazing job of matrixing stereo into 7.1.

PLIIx music, if set up correctly doesn't sound too shabby either.