# Do i need to add delay to side channels?



## StabMe (Nov 17, 2011)

So i am using a CarPC. Description of my build can be found here.

Basically, i am using a 10 channel interface, have a 3 way front, central channel, rears and a sub. DSP is being done in Audiomulch.

I am toying with V.I Stereo to 5.1 converter VST. I like how it does stereo to LCR. But a bit confused on adding rears.

In a huge MS-8 thread, Andy said that in MS-8 he has rear channels delayed a bit, that is, after he has them time aligned.

All my speakers are time aligned. Now, do i have to add some additional delay for rear speakers in order to use the rear fill generated by this VI plugin?


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## Ge0 (Jul 23, 2007)

StabMe said:


> So i am using a CarPC. Description of my build can be found here.
> 
> Basically, i am using a 10 channel interface, have a 3 way front, central channel, rears and a sub. DSP is being done in Audiomulch.
> 
> ...


I know this thread is almost 2 years late. But, the answer is yes. You want to add delay to rear channels to liven up your listening room to make it sound more realistic. And here is why. 

When you listen to live music you sit in a larger room than a car. Front facing sound hits you a a rate of 3mS per meter. Say you are relatively close to the stage. Say, 5 meters away. It takes 15mS for the front wave to hit you. But, that frontal sound wave passes you and continues to travel until it hits a rear surface. It then reflects off the rear surface and travels back to you. Say the rear wall is 15 meters behind you. The frontal wave would travel 30 meters before it hit a rear wall and reflects back to you. 30 meters times 3mS is 90mS. This sets a room atmosphere or limit. Your brain makes this sound natural. Also keep in mind that the reflecting sound will be attenuated as any sound does over distance. More in high frequencies (with less energy) than low frequencies.

Now translate this to a vehicle. You sit 1 meter away from the sound source. The front wave hits you in 3mS. The rear reflections pass you and bounce back roughly 6mS later. This listening space is small and seems unnatural. How can you liven up your listening space? Delay the rear signal so it bounces back later to make the room sound larger. Don't get carried away though. Slight adjustments can go a long way. Too much delay will make your listening space sound like a cheesy church simulation on your old home theater receiver. Also make sure the rear channels are attenuated and low pass filtered to try and closely replicate real physics.

Back in the day I used to subtract left from right stereo signals to filter voice out of the reflected audio and only leave far left and right content. This would minimize confusion with the artificially generated stereo front stage image. This is not as important if you have a dedicated center channel that nails a front stage center image. If still running a 2 channel front stage then still consider L-R rear fill. This is not as difficult as it used to be due to DSP. Analog manipulation is tougher to get the right affect.

It's up to you to try this stuff out and judge results for yourself. Good luck and ask for help if you like. I've used this method on many home and car systems for years and stick by it.

Ge0


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## StabMe (Nov 17, 2011)

Wow, thanks for chiming in 

Yeah, i agree with all that you say. Delay is necessary, sure. I was just wondering if V.I Vst plugin delays the sound a tad on its own or not. I have a few presets, some with added delay, some just raw. Can't say i feel much of a difference.

I also use NuGen Halo upmix VST plugin - this one has tons of controls and sounds better for my taste. It's more CPU hungrier, though. Especially when you have so many channels with FIRs.


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