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4 Replies Last post: Oct 28, 2008 11:55 AM by ImageaProductions

Has anyone created a program to fake surround sound with a Nexia?

Oct 5, 2008 9:07 AM

Click to view eyeloot's profile eyeloot 5 posts since
Sep 18, 2008
I have a theater room I would like to use a Nexia PM in. I would like to simulate 5.1 surround sound. Has anyone done this or have any suggestions how it might be done?
Tags: nexia, surround, theater, 5.1
Click to view Yeah's profile Yeah 42 posts since
Jan 14, 2008
1. Re: Has anyone created a program to fake surround sound with a Nexia? Oct 7, 2008 3:16 AM

Hi Edgar


As AC-3 Dolby Digital and DTS systems are fed with individual channels (5.1 / 7.1) you cannot really simulate this. The tracks are mixed and "spread" into these channels with individual audio... handling a surround system with Audia / Nexia means you need the 6 in- and Outpts on the DSP, the feed can come straight out of a DVD or BlueRay Player with direct outs - there are many on the market. "Simulating" with a stereo source could be a frequency cut (High Pass and LowPass) on the center channel (mix of L&R) to mainly have the voice on it and then some delay on the rears (same channels as L&R) to create a certain room feeling but it will never sound good nor give you that cinema sound you would expect.

A Nexia PM can do the job very well but all the outputs will be needed for the Speaker Outs.

Cheers

Chris

Click to view AVDocumentSolutions's profile AVDocumentSolutions 14 posts since
Sep 23, 2008
2. Re: Has anyone created a program to fake surround sound with a Nexia? Oct 7, 2008 8:33 AM

I found a website that crudely explained some of the processing to make a pseudo-quasi surround system from a stereo feed. I'm pretty sure it won't sound nearly the same as the real thing. However, I made the attached Nexia file just for the fun of it anyway. I don't have a unit in-hand to see what it sounds like, so no promises.

Here's what I've done: Left and Right go thru 2-way cross-overs to separate the bass. They are then fed into a mixer that combines the two channel's lows and feeds them to the sub. The left/rights feed thru and are also mixed together, attenuated 6db then sent to the center speaker. There are two notches recommended at this site that I put in also. The surrounds get tricky. By inverting one of the feeds and mixing it with the other feed, you cancel out most of the spoken words. What I did was replicate this process four different ways that would hopefully keep some of the stereo sound. I gradually lowered the level of each feed and added more and more delay. I then mixed the four sets down to one stereo set. These feeds are fed into primary delays for the rear. I'm hoping that the redundant signals will give a slight reverb-esk sound.

Yes, it's crude. But hey, maybe it might pass if you just need something close, but can't afford a true processor. If you do try this out, please please please tell me how horrible or good it works out for you.

James Shaffer, CTS

AV Document Solutions, Providing support services for AV contractors

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Click to view yanesan@gmail.com's profile yanesan@gmail.com 1 posts since
Sep 18, 2008
3. Re: Has anyone created a program to fake surround sound with a Nexia? Oct 8, 2008 6:51 AM
in response to: AVDocumentSolutions

I can't rememer where I found it, but you can google the algorithm for Dolby Pro Logic decoding. The center is L+R highpassed, the rears are delayed with the L or R mixed with the opposite channel inverted, the sub L+R lowpassed. The only part that wasn't readily apparent was the dip at 3khz for the center channel -- for some reason that really takes the harshness out of the center.

This is an implementation i did for a theater in a gymnasium. It was created because some DVD's don't default to 5.1 channel sound, but to 2 channel pro logic. I've removed the extra logic that involved automatically detecting 5.1 surround from the DVD player and switching to pro logic when 5.1 is not provided. There's still some extraneous stuff in the program, but it's still not too hard on DSP resources -- not intoducing too much processing delay was a concern to keep the lips on the screen synced with the sound. The compressors were a concession to trying to do surround sound in a very noisy room full of treadmills and excercise bikes -- the wide dynamic range that movie soundtrack designers are enamored of was a detriment in this setting!

If you just want general purpose surround, try googling "hafler surround"

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Click to view ImageaProductions's profile ImageaProductions 2 posts since
Oct 28, 2008
4. Re: Has anyone created a program to fake surround sound with a Nexia? Oct 28, 2008 11:55 AM

The Nexia would be best used as an equalizer in a theatre system. In general the processing that goes into the different formats of theatre and surround sound is proprietary and done in a processor. Then from the processor goes into a DSP such as the l

London Blu 16 or in this case a Nexia for room equalization. This is how the JBL Synthesis System is and is what is used in THX certified theatres. I use the same DSP for live sound that they use as an EQ.

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