# Is Rear Fill (and center channel) helpful or hurtful in a car?



## KillerBox (Jan 7, 2011)

I would like to start a thread about the discussion of rear fill and center channels in car audio system. I know a lot of people say rear fill and center channel are unnecessary or detrimental to their sound stage.

I for one love Rear Fill when it is done right especially with a surround sound processor. I feel like it helps widen my sound stage and provide some ambiance like you would hear at a live concert. 

Article on how to add rear fill in car: https://drive.google.com/open?id=1cx8fWOM8DTfmvzMCzCfYLcPNT4WzpzLw

Article on how to add center channel speaker in car: https://drive.google.com/open?id=17AKh3lc_n2MdJSZV5M1elBdLC1csl940

Article on 2 channel stereo vs. surround sound in car: https://drive.google.com/open?id=1mf8ae_M4velGuQVeydVkfXeoc4xvf98G

Article on how to set up a proper soundstage in car: https://drive.google.com/open?id=1Hu1hq5_M1zdRhCjPmCD6C8yhiGPwc_hp

PassMag Article on JBL MS-8: https://drive.google.com/open?id=12l2jrqHxuNEBVhBjbgfPNVAUUkta5WoI

Fosgate Gavotte (car stereo surround sound processor that started it all in the early 1980s) https://drive.google.com/open?id=1U6Sva-yu9WxOtSWCFdxeuRtNtOrC4CoN

AudioControl ESP-3 Manual: https://drive.google.com/open?id=1rQ838gYnuvMU5q0xupLixDCUWsX8YLkM

I know Alpine and others had Surround Sound processors but, I don't have any information on them.

It seems to me that factory OEM systems are coming more with surround sound processors and the aftermarket systems are lagging behind.

Please free to add an articles or other information that either helps prove or disapprove that rear fill helps. P.S. I would like to thank and acknowledge the writers of these articles!


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## SkizeR (Apr 19, 2011)

I didn't read them, but these articles are 25 years old. Things have changed and technology has greatly improved, so no matter what they may or may not say, I would take it with a grain of salt. 

That said, in order to execute a center channel PROPERLY you need a processor with an upmixer. The Alpine h800 is the only one that I know of currently in production that offers this.

Rear fill is a bit easier. What you want to do is simulate the echo of a larger room. You do L-R signal routing on the rear speakers, bandpass them, attenuate them, and heavily delay them. There's a hand full of processors that can do this.



Are they helpful or hurtfull.. Well either done right shouldn't hurt. A properly executed center channel will give stereo imaging from two seats, not just single seat. Rear fill isn't that hard to help improve the overall feel and ambience of the system. A standard stereo system is easier though if your only concerned about the sound from the drivers seat.


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## FordEscape (Nov 23, 2014)

Opinion from an MS8 user with no other DSP experience.

As far as rear fill I've never felt it distracted from or was detrimental to my front stage. I like the ambience that Logic 7 with rear fill provides, but accept that some don't care for it, no worries (though I gotta wonder if they're listening to well-implemented and tuned rear fill). With some recordings the effect is more apparent than others, but always a subtle enhancement for me. When I turn off processing it all goes south in a big-bad way but admit I've not really focused on trying to achieve a great tune in that mode.

As far as the center.... I ran without for a long time and had a great front stage for driver only occupancy. Early efforts with an added center were a bit frustrating, seeming to pull my stage a bit closer for driver only. Adding broader frequency capability to the center (went 2-way) and tweaking both levels and XOs now have me happy with the center, even when alone in the car. No question in my mind at all that a superior 'second-occupant experience' is facilitated with the processed center and as things stand now after a fair amount of tuning I don't feel the 'driver only' experience is compromised.

IMHO SkizeR nailed it with the comment about proper upmixing being an essential element for any _chance_ of a good 'with center' listening experience. From that starting point all the usual tuning efforts come into play to optimize for a particular cabin. For me it all goes totally south with the processing defeated .... I can't imagine achieving a good effect with a center but without the MS8 L7 processing / upmixing (or similar, at least in concept as I understand it, Alpine H800 Dolby center processing / upmixing).

I'm not sure it's reasonable to damn or praise rear fill or (even 'properly upmixed') center channels just on face. IMHO the devilish details that make-or-break the proposition are, as with most other 'traditional' arrangements, in the tune.


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## SkizeR (Apr 19, 2011)

Another key to a good center channel that many don't realize is that you need a lot of cone area. A lot more than the standard 3" opening that is in most cars. You want it to play down to at least the mid to low 100's hz.

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## beak81champ (Oct 2, 2015)

SkizeR said:


> Another key to a good center channel that many don't realize is that you need a lot of cone area. A lot more than the standard 3" opening that is in most cars. You want it to play down to at least the mid to low 100's hz.
> 
> Sent from my SM-G950U1 using Tapatalk


So, if I’m running GB25’s and 10’s in my pillars, I would want to use a 4” as a center? Would I also need a center tweeter? Maybe a coax? I’ve never heard a car with a center channel, so this is intriguing.


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## Elektra (Feb 4, 2013)

SkizeR said:


> I didn't read them, but these articles are 25 years old. Things have changed and technology has greatly improved, so no matter what they may or may not say, I would take it with a grain of salt.
> 
> That said, in order to execute a center channel PROPERLY you need a processor with an upmixer. The Alpine h800 is the only one that I know of currently in production that offers this.
> 
> ...




The helix can do rear fill right? 


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## SkizeR (Apr 19, 2011)

beak81champ said:


> So, if I’m running GB25’s and 10’s in my pillars, I would want to use a 4” as a center? Would I also need a center tweeter? Maybe a coax? I’ve never heard a car with a center channel, so this is intriguing.


Put it thisbway, Andy W is running a pair of gb40s (which have a recommended high pass of at least 110 @ 12db) and a gb10 for his center channel.

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## ErinH (Feb 14, 2007)

I think this is one of those things where you just have to try it (and do it right) before you'll know. 

I've messed around with rear fill a few times over the past 7-8 years. Ultimately, though, I'm not a huge fan. There's the delicate balance of blending the output level of the rear fill to that of the front speakers and even when you get it right, there will be instances where you'll find it as a distraction. IMO the music you listen to will be a prime factor in how you feel about it. It can help with some tracks but it can also hurt; namely on tracks where the info is panned to the extreme ends of the soundstage and will pull, by nature of the difference signal, in the center behind you. If you drop the levels to avoid this then the *other* times it wouldn't matter... the signal is just too low to make any impact. 


As for center channels, as has been noted, you really need a good upmixer to handle the signal and steer accordingly. Using summed mono (L+R) for center will hurt the width of the soundstage, namely in the midrange. And with regards to it being the perfect solution for 2-seat listening, I'm still on the fence.


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## ErinH (Feb 14, 2007)

Elektra said:


> The helix can do rear fill right?
> 
> 
> Sent from my iPhone using Tapatalk


Yes. You do this on the input matrix. Add the left input and right inputs together. Then flip the polarity of one of them (whichever you want to subtract) by double-clicking on it and setting the polarity to 180 deg. You'll have to set this up on two output channels and you'll have: L-R and R-L signals from those outputs.


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## KillerBox (Jan 7, 2011)

I am running two Focal ES 4" and two 1" as my center channel speakers. Crossed over @ 200hz @ 24dB. 

I probably could have crossed them over a little lower hz but, I am overdriving them to keep up with my door speakers.


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## beak81champ (Oct 2, 2015)

Would the new jl vxi amps, and the HUB involved, make it possible, or even easier to do a center and/or rear fill? The info upon rollout made it seem as if there are almost endless possibilities and configurations using these amps.


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## Elektra (Feb 4, 2013)

ErinH said:


> Yes. You do this on the input matrix. Add the left input and right inputs together. Then flip the polarity of one of them (whichever you want to subtract) by double-clicking on it and setting the polarity to 180 deg. You'll have to set this up on two output channels and you'll have: L-R and R-L signals from those outputs.




Thanks Erin - just curious may or may not use it... more for the kids in the car really...


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## ErinH (Feb 14, 2007)

beak81champ said:


> Would the new jl vxi amps, and the HUB involved, make it possible, or even easier to do a center and/or rear fill? The info upon rollout made it seem as if there are almost endless possibilities and configurations using the amps.


The vxi doesn't have upmixing; so there is nothing more than simple addition/subtraction. Which means no 'steering' for center and sides. You can do difference signals on the input matrix, though, to achieve the rear fill effect.


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## ErinH (Feb 14, 2007)

Elektra said:


> Thanks Erin - just curious may or may not use it... more for the kids in the car really...
> 
> 
> Sent from my iPhone using Tapatalk


If you're doing it for the kids, I'd just stick with regular ol' stereo. The (differential) rear fill will sound weird to them (if you haven't heard it, set it up and listen and you'll see what I mean). Just run the rears as standard left/right for the kiddos.


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## Elektra (Feb 4, 2013)

ErinH said:


> If you're doing it for the kids, I'd just stick with regular ol' stereo. The (differential) rear fill will sound weird to them (if you haven't heard it, set it up and listen and you'll see what I mean). Just run the rears as standard left/right for the kiddos.




Yeah God forbid if Ed Sheeren sounds a bit off... lol! 


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## KillerBox (Jan 7, 2011)

I have tossed around the idea of using a MS-8 or another upmixer with the new vXI amps but, I am so happy with my current system that I see it being at the point of diminishing or non returns.


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## ErinH (Feb 14, 2007)

Elektra said:


> Yeah God forbid if Ed Sheeren sounds a bit off... lol!
> 
> 
> Sent from my iPhone using Tapatalk


Haha.

Well, it's not even that ('a bit off'). It's a very odd effect. I wouldn't even describe it as a 'echo'... just a very weird effect.

In nominal usage it's level is low so that you barely discern it. But since the kids would be closer to the rear speakers than they would be the front they'll likely hear the rears as twice as loud... so all that... 'mess'... will override the 'normal' stereo sound. So, yea, if you're doing it for them to hear music or video or whatever, I'd stick to regular stereo in the rears.


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## Elektra (Feb 4, 2013)

ErinH said:


> Haha.
> 
> 
> 
> ...




Thanks Erin for the input and advice...


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## JH1973 (Apr 21, 2017)

My current set up has no rear fill,just active 2-way.I haven't tried using the rear fill that's available from my HU and stock rear deck speakers.Maybe I'll open the trunk and plug the speakers in to see how it sounds.

Barring a few annoying rattles,I am very happy with how my stuff sounds and the imaging is still something I can't believe.Vocals coming from dead center of my windshield and majority of instruments on sides of dash.There's a slight bit of rainbowing but not enough to bother me.I haven't touched my tune since November and really don't want to.I'm so glad I finally listened to people here and got a DSP.Compared to passive it is night and day!


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## FordEscape (Nov 23, 2014)

In regard to rear fill would like to add that for _me_ (with an MS8) it was important to realize that the fill needed to be very subtle for IMHO best effect. When tuned so it was 'readily apparent' it wasn't nearly as satisfactory as when tuned to a level that I almost didn't notice it was there until I switched it off.

Struggling to find the words to explain .... for me rear fill works best solely as an ambience enhancer, not as an immediately perceived apparent additional sound source, if that makes any sense. 

And I do agree with ErinH's suggestion that it's highly dependent on the recording .... I over-reached when I said in my previous post that it's "always" an enhancement. Better to have said it's _usually_ an enhancement with the music I listen to.

As far as the center, I certainly wouldn't say it's the panacea or perfection for two-seat listening (certain I've not encountered either). But IMHO with proper upmixing and tuning it does increase the probability of achieving a _better_ two-seat listening experience than a no-center system provides in the small confines of a car cabin.

I've wondered if some sort of arrangement of multiple discrete L&R (only) channels and speakers could do better, somehow creating an almost headphone-like 'capsule of sound' around each separate occupant in a car cabin, working with the frequencies that are most 'locatable' in human hearing and perception. But I digress .... that's far from an approach supported, I suspect, by any of the 'produced for car audio DSPs' currently on the market.


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## seafish (Aug 1, 2012)

FordEscape said:


> I've wondered if some sort of arrangement of multiple discrete L&R (only) channels and speakers could do better, somehow creating an almost headphone-like 'capsule of sound' around each separate occupant in a car cabin, working with the frequencies that are most 'locatable' in human hearing and perception. But I digress .... that's far from an approach supported, I suspect, by any of the 'produced for car audio DSPs' currently on the market.


Your talking about ambio sound and IIRC one of the current oem "high end" sound systems IS using headrest mounted L+R speakers. But you are right, it is complicated to properly implement. Patrick Bateman has posted more then one thread about it.


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## naiku (May 28, 2008)

Elektra said:


> Yeah God forbid if Ed Sheeren sounds a bit off... lol!


Haha :laugh:



ErinH said:


> Well, it's not even that ('a bit off'). It's a very odd effect. I wouldn't even describe it as a 'echo'... just a very weird effect.


Yup, it is a really weird effect. Hard to even explain it until you hear it to be honest, it's like you only hear parts of a song.

Personally, I like it. I used to run an MS8 with a center, but the biggest center I could fit was a 2" driver and for me, it would narrow the stage. I have run rear fill with the rear speakers positioned low in the rear door cards and now run them up at the sides of the cargo cover. Having them higher makes a good improvement over them being low down.

As above though, a lot depends on not just install but personal preference. The effect is more noticeable on some songs than others and a lot of the setup comes down to trial and error.


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## Bnlcmbcar (Aug 23, 2016)

I’ve been toying around with the TA and EQ on my stock headunits DTS Neural upmixer. So far like others have said it’s good for some songs and not for others.

Does any one have any info on Alpine’s (proprietary?) surround upmixer: Euphony found on the H800?

I haven’t been able to dig much info on it and how it differs from Dolby Prologic II or Logic 7.

I think oabeieo has it right that an upmixer (H800 or MS8) fed into a MiniDSP DDRC88 to correct these “home” and “movie” upmixing algorithms for the car envioronment would yield the best results.

Haven’t tried it yet myself but I bit the bullet and purchased an Outlaw 975 (the smallest home AV processor with a myriad of upmix processing options that I could find) to experiment with once I get better aquainted with the Dirac system.

As far as 2 seat tuning with a center channel, I’m patiently waiting for Dirac to open up their algorithms for use at the automotive consumer level (only available for OEM implementations at the moment) but the possibilities seem interesting:

https://www.dirac.com/dirac-virtual-center/

^ That or Andy’s Penteo upmixer whenever it comes to fruition.


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## -Kyle- (Feb 5, 2009)

Sorry if this is a little off topic, do we have much info on the new Audio Frog DSP? I saw someone mention it in a post but haven't seen much else. I assume it will work well with a center channel like the MS8 did/does?


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## Romey (Jul 4, 2014)

I was running an Audiofrog GS60 and GS10 for a center channel with an MS-8.
It was my first and only experience with a center channel in a vehicle and I liked it. It did take some getting used to though.


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## JimmyDee (Mar 8, 2014)

I've never been interested in doing a Center Channel... but I have always done Rear Fill.
Just personal preference...

As SkizeR mentioned; it's a bit of an _'art form'_ to get rear fill to sound good.
Trust me... I've done plenty of trial and error (mostly error), before perfecting it.

If done right; it can sound very good (IMO).
If done wrong; it can make your sound stage A.F.U.


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## 156546 (Feb 10, 2017)

Center needs to be 200Hz-20k. Lower is better, but 200 Hz is a must.


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## rton20s (Feb 14, 2011)

I guess it is good to see another thread about rear fill, center channels and upmixing. There have been A LOT of discussions on these various topics, going back to the beginning of this site. In fact, some of the best info for rear fill goes back more than a decade. And there have been a lot of recent discussions regarding upmixing, and how to do it from a "flat two channel source" and how/when you might to take advantage of the upmixing/surround capabilities of OE systems. From personal experience, I have heard cars with no rear fill, cars with rear fill and cars with upmixing and center channels that all sound excellent. And all of them capable of, or even being world champion level SQ cars. 

In my own car, I don't ever see myself implementing an upmixer or center channel. The dash is not designed for simple integration of a center channel, I am almost always in the car alone, and it is the car I use to compete. However, I am pretty likely to play around with rear fill in the future. If for nothing else, to see how it well it works in my specific vehicle. 

Looking to my wife's car, use of an upmixer and center channel is likely to remain in place. I state it that way because the car came equipped with an OE DSP amp that supports 8 output channels and 11 speakers. That includes a center channel, rear doors and rear deck drivers. The fact that I am usually a passenger in the car, and the fact that I haven't had a system like this before, has me interested in pursuing an upgraded version of this "surround sound" system. That set me on a research path that turned up some very good information from extremely knowledgeable industry sources. 

First, there is a great article series called "All Mixed Up" in Mobile Electronics Magazine from Joey Knapp (Introduction), David MacKinnon and Andy Wehmeyer (Nov/Dec 2017). These articles give a great rundown on how modern automotive upmixers work, including the distinction between matrix (Dolby Pro Logic 2 & Harman Logic 7) and non-matrix upmixers (Harman Quantum Logic, Bose Centerpoint, Audiofrog Multi-seat/Penteo Perfect Surround). They also include a very brief history on surround sound/upmixers and the roots in film. Finally, Andy walks through the steps of his approach to upgrading a factory system with an upmixer. 

https://issuu.com/mobileelectronics/docs/17me_november
https://issuu.com/mobileelectronics/docs/17me_december

I was also fortunate enough in doing my research and talking directly with Andy (Hi Andy!) to discover that Ken Ward (Musicar NW) had actually performed a similar, simplified system upgrade to what Andy described in the article on the very vehicle my wife now drives. A 2017 Mazda 6 with the Bose Centerpoint system. (The wife's is a 2015, but has the same audio system.) Not only had he done the upgrade, but he also wrote an article about it for CE Outlook. The addition of a DSP amp (Match 86DSP) was enough to provide some additional output from the OE system while providing enough EQ to address any trouble areas. 

https://www.ceoutlook.com/2017/05/17/installer-tip-working-factory-upmixer/

In addition to the information found in the links above and some recommendations directly from Andy, I took a flyer and reached out to a BOSE engineer as well. His recommendation is somewhat the inverse of the tack suggested in the links above. For the Bose Centerpoint systems, he actually recommends upgrades in the following order. 1. Upgrade Drivers. 2. Upgrade Amplification (after OE DSP amp). 3A. DSP for Tonality Adjustment (before DSP amp). 3B. DSP for Driver FR Correction and Tonality Adjustment (after OE DSP amp). 

It actually gets a bit more complicated than that, but one of the issues with the Bose Centerpoint system is that it makes use of "Dynamic EQ which is the Bose version of loudness restoration." And that Dynamic EQ isn't based on volume position, but rather input level which means it is constantly adjusting low frequency boost. So, no simple "set it and forget it" with the OE head unit volume level and using the level adjustment on the DSP. That is certainly one of the hurdles to get over, but one I think can be worked around with a little creative thinking and integration.


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## Bnlcmbcar (Aug 23, 2016)

Thank you rton20s for the articles!::surprised:
Always good to have these nuggets of knowledge!



rton20s said:


> For the Bose Centerpoint systems, he actually recommends upgrades in the following order. 1. Upgrade Drivers. 2. Upgrade Amplification (after OE DSP amp). 3A. DSP for Tonality Adjustment (before DSP amp). 3B. DSP for Driver FR Correction and Tonality Adjustment (after OE DSP amp).


^This is the approach I have currently taken with my 2016 civic’s DTS Neural headunit which as to what I can gather is a DTS NEO variant that upmixes 2.0 stereo to 5.1 surround. iPad digital source is inputed via USB to the headunit and all the DTS processed speaker level signals from the car amp routed into my Helix DSP where I can:

-Counter the stock speaker EQ. 
-Minimally adjust T/A as the signals are already time aligned for the 10 stock speaker locations.

Luckily the Civic headunit has an option to defeat the Speed Volume Compensation feature so I have no need to worry about levels changing while driving.

Current center channel is a 3.5” JL C2 coaxial crossed down to 275hz. So far I’m pleased with having the option to offer a better than stock sonic experience for more than one person when commuting with passengers. 

It comes down to personal preferences. I view it as a different ‘stage’ per se. 2.0 stereo giving one a potentially wide performance from the artist or musicians musicians staged in front of you.. 

where as surround upmixers can emulate that same experience for more than one seat or give you a different stage that emulates one being the artist or musicians on a stage performing with instruments playing around them.:guitarist:

*Are the majority of tracks recorded for a surround experience? No
*Was this the intention of every artist for the surround listening experience? No
*Does it require expensive gear? Yes
*Does it require a stout center channel? Yes (either fellow user seafish or I will eventually get around to installing our shared purchase of component set so that we can each run a passive Morel Virtus Nano 2way on the center dash.. should be good down to 80hz at least)
*Aren’t these all gimmicks that modify the recorded purity of the signals? Yes (maybe not Penteo which claims to eliminate phase artifacts)
*Can it sound awesome and enjoyable? Yes


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## ErinH (Feb 14, 2007)

Bnlcmbcar said:


> ^This is the approach I have currently taken with my 2016 civic’s DTS Neural headunit which as to what I can gather is a DTS NEO variant that upmixes 2.0 stereo to 5.1 surround.


Interesting.

Is this something you can defeat if you preferred not to use it?


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## Ziggyrama (Jan 17, 2016)

Question, if my DSP can only do L+R summing, can I simply swap polarity on the R channel at the input side to achieve L-R?

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## Bnlcmbcar (Aug 23, 2016)

ErinH said:


> Interesting.
> 
> Is this something you can defeat if you preferred not to use it?


Yes. I can turn off DTS Neural setting and everything from the headunit comes out in Stereo.

However for fidelity sake, with my 1 seat stereo tune I use a USB to Coax converter sending iPad signal directly to SPIDF Coax input on the Helix.


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## Elektra (Feb 4, 2013)

I remember asking Audiotec Fischer the question about the center channel...

They were convinced the DSP PRO can do a Center channel..

I’ll need to dig up that email...

Or I may just ask Julian Fischer about this again...


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## 156546 (Feb 10, 2017)

Elektra said:


> I remember asking Audiotec Fischer the question about the center channel...
> 
> They were convinced the DSP PRO can do a Center channel..
> 
> ...


L+R is NOT an effective center channel.


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## SkizeR (Apr 19, 2011)

Elektra said:


> I remember asking Audiotec Fischer the question about the center channel...
> 
> They were convinced the DSP PRO can do a Center channel..
> 
> ...


It can. Just not an upmixed center channel 

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## Elektra (Feb 4, 2013)

SkizeR said:


> It can. Just not an upmixed center channel
> 
> Sent from my SM-G950U1 using Tapatalk




Yeah I read that email it does do it just depends on how you perceive the center channel and what you consider a proper center...

I did email Julian as well - curious to see what he says as well...

If it’s anything worthwhile I’ll post it up...


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## Bnlcmbcar (Aug 23, 2016)

Helix DSP Pro currently has no processing or steering for center channel other than a mono sum of (R+L) via the IO matrix. One can alter the ratio of the mono sum like 30%L + 70%R or whatever you desire.

Maybe the Helix DAC compontents are powerful enough to run an upmixer (many other DSP units ‘technically’ could as well) but the Helix product has no licenses to currently do so.


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## SkizeR (Apr 19, 2011)

keep your eyes open though


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## Rainstar (May 22, 2017)

I'm having Skizer do 3 way Rear fill in the next few months. Posing a huge challenge to one of the best on here. So much info to read over and overcome skepticism about running Rear fill. I think I should do it just for the reason alone that it is Hard. Lets tackle the hard **** head on.


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## SkizeR (Apr 19, 2011)

Rainstar said:


> I'm having Skizer do 3 way Rear fill in the next few months. Posing a huge challenge to one of the best on here. So much info to read over and overcome skepticism about running Rear fill. I think I should do it just for the reason alone that it is Hard. Lets tackle the hard **** head on.


yeah, thanks for the challenge :laugh:


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## 156546 (Feb 10, 2017)

SkizeR said:


> keep your eyes open though



What?


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## Bnlcmbcar (Aug 23, 2016)

^What Andy said!



SkizeR said:


> keep your eyes open though


If no “WHAT”... How about a general “WHEN” should we keep our eyes open...

Sometime in the near future doesn’t count


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## SQ Audi (Dec 21, 2010)

SkizeR said:


> Are they helpful or hurtfull.. Well either done right shouldn't hurt. A properly executed center channel will give stereo imaging from two seats, not just single seat. Rear fill isn't that hard to help improve the overall feel and ambience of the system. A standard stereo system is easier though if your only concerned about the sound from the drivers seat.
> 
> 
> Sent from my SM-G950U1 using Tapatalk


Question Nick. If one were to put in wide band drivers in the center channel, with a small 2 channel amplifier, no crossover, and just tune the gains to match the rest of the system, would this help in creating a better center image from either seat? Asking for a friend.


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## SQ Audi (Dec 21, 2010)

GotFrogs said:


> Center needs to be 200Hz-20k. Lower is better, but 200 Hz is a must.


So a really stout wideband will do the trick?


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## gijoe (Mar 25, 2008)

SQ Audi said:


> So a really stout wideband will do the trick?


Probably not. A wideband will not produce the high freqquencies off axis, and you'd probably need a pair to get down to 200hz.


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## SkizeR (Apr 19, 2011)

SQ Audi said:


> So a really stout wideband will do the trick?


A wideband would most likely create issues as a center if your left and right follow a traditional omnidirectional setup. 

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## durwood (Mar 7, 2007)

For rear-fill I would start with midbass only rear-fill. It will aide in fixing the lopsided azimuth angles and also help correct room mode nulls. It's a two-fer improvement. The car is a small room that pushes room modes into midbass territory. HT guys use multiple subs to fix room modes in medium to larger rooms, but our room is smaller.

It does work, I suggested to a friend to do in in his golf R simply using stock locations and he was surprised. I view him as someone who has tuning abilities and works with this stuff everyday beyond my rather hobbyist dabbling, so surprising him with this concept was cool. Gain and filter frequencies do have to be played with. He has also played with Hafler rear fill (L-R, delayed, gain) way back in the 90's, but he had never considered something simpler.

I believe werewolf once also suggested mid-bass arrays, and there was a thread here on it, but I don't remember it covering the room mode aspect of it. That is probably the main benefit, and fixing azimuth errors via vector summation is just a side benefit.


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## Ziggyrama (Jan 17, 2016)

durwood said:


> For rear-fill I would start with midbass only rear-fill. It will aide in fixing the lopsided azimuth angles and also help correct room mode nulls. It's a two-fer improvement. The car is a small room that pushes room modes into midbass territory. HT guys use multiple subs to fix room modes in medium to larger rooms, but our room is smaller.
> 
> It does work, I suggested to a friend to do in in his golf R simply using stock locations and he was surprised. I view him as someone who has tuning abilities and works with this stuff everyday beyond my rather hobbyist dabbling, so surprising him with this concept was cool. Gain and filter frequencies do have to be played with. He has also played with Hafler rear fill (L-R, delayed, gain) way back in the 90's, but he had never considered something simpler.
> 
> I believe werewolf once also suggested mid-bass arrays, and there was a thread here on it, but I don't remember it covering the room mode aspect of it. That is probably the main benefit, and fixing azimuth errors via vector summation is just a side benefit.


Very interesting. Where would you recommend to set the low pass filter?

Sent from my Pixel using Tapatalk


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## 156546 (Feb 10, 2017)

SkizeR said:


> A wideband would most likely create issues as a center if your left and right follow a traditional omnidirectional setup.
> 
> Sent from my SM-G950U1 using Tapatalk


IF a wide band is pointed at the windshield, the high frequencies that are only present in the on axis sound will be reflected off the windshield and it'll seem more like it has a tweeter. This is why many of the new OE systems use a small 2" in the dashboard. Works fine. Tweeter is better, but...


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## rton20s (Feb 14, 2011)

GotFrogs said:


> IF a wide band is pointed at the windshield, the high frequencies that are only present in the on axis sound will be reflected off the windshield and it'll seem more like it has a tweeter. This is why many of the new OE systems use a small 2" in the dashboard. Works fine. Tweeter is better, but...


I was thinking the same thing. Quite a few competitors who have done the same thing with "wide band" or "full range" drivers. This is also the approach Bose takes with the center on a lot of their cars. (Shocking, I know!) For instance, this is what I'll be dealing with in the Mazda 6 my wife has.


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## Elektra (Feb 4, 2013)

For those interested - Audiotec Fischer responded today regarding my mail about if there DSP products can do a center channel...

So here is there response..

Hi Massimo,

up to now in all our DSP devices it is possible to make a center channel as a summation of the left and right signal. Theoretically this is the right center channel signal when you only have a left and right signal as a source. 
Nevertheless there are upmixing algorithms like Dolby ProLogic, Logic7, etc. which are using a stereo signal and doing complex mathematics to create a new signal which is only reproducing the mid information of the stereo signal. This is usually called "steering". 

We have also been looking for a proper center channel processing during the last years but did not find any solution which worked out as intended. So we started to research and develop an own center channel upmixing which was now firstly released in our MATCH UP 7BMW amplifier and will be included in most of all upcoming DSP products. Unfortunately due to its concept and the big amount of processing power which is needed it will not be possible to offer this as an software update for the actual DSP generation. 
Our new self-developed algorithm is called "RealCenter" and provides a steering center channel signal which highlights just the mid information of the stereo signal. 

Nevertheless just from a theoretical standpoint the correct center channel is still the summation of the left and right signal but in fact this concept has some disadvantages in the car as the typical center channel makes the stage much more narrow and the focus is heavily concentrated above the center channel. Therefore an upmix algorithm is needed if you don't want to affect the width of the staging but have at the same time a staging for the driver and passenger seats.

Best regards

Julian Fischer



Sent from my iPhone using Tapatalk


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## durwood (Mar 7, 2007)

Ziggyrama said:


> Very interesting. Where would you recommend to set the low pass filter?
> 
> Sent from my Pixel using Tapatalk



I'd start around 250Hz and go up/down from there, I like shallow slopes so it it is a gradual fade out rather than a hard cut, but YMMV. I will have to ask my friend what he settled on if he remembers.


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## 89grand (Nov 23, 2006)

The stock Boston stereo in my Magnum sounds a lot better with the rear 6x9 speakers playing. You don't notice them...until you turn them off, then the center image and sense of space turns to ****, and sounds really 2d. That's why I am going to use rear speakers in my current build in that car.

I'm just going to use some cheap Pioneer 6x9 coaxials, and band width limit them to something like 200-3000hz, or whatever ends up sounding the best, but they won't be playing full spectrum.


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## 156546 (Feb 10, 2017)

In response to the earlier post about upmixing, there are some misconceptions here.

First, Julian is right that a L+R center narrows the stage. The reason is simple. If the center and the right play the right only information at the same level, then the image for "right" will appear in between the center and the right. That works the same way as a phantom center does--when the right and the left speakers play the same thing, then that image appears in the center.

Matrix processors like Logic 7 and Dolby PL2 use a L+R center. To counteract the stage narrowing problem (to keep the stage as wide as possible), they use a steering matrix which calculates a "steering angle" and that calculation is fed to a bunch of automatic level controls that turn channels up and down really quickly. So, if a signal is steered to the center, the right and the left channels are attenuated. If a signal steers right, then the center and the left are attenuated. 

Because the ENTIRE signal is turned up and down, these algorithms don't do a very good job of resolving the location of transient sounds while there's a steady state sound in the background. This causes steering errors.

The rear channels in these processes use a difference signal. So, if a sound is the same level in the right and left channels but it's 180 degrees out of phase, it steers rear. This was originally intended to make it possible for someone who was mixing a MOVIE to encode the rear channels onto a 2-channel medium. 

Music isn't mixed for upmixers like this, so the difference signal in the back is sometimes annoying--speakers turn on and off and if there's no out of phase information in the track and very little left or right only information, then the rear speakers don't play. That's sometimes annoying for people who want to hear stuff coming out of their rear speakers. 

These algorithms don't steer only midrange to the center speaker, they steer the full frequency band unless some other limit is placed on the steering. Often, the low frequencies that are steered center but that occur below the center speaker's cutoff frequency are steered back to the left and right main speakers. Center sound below the left and right speakers' high pass filter are sent to the sub. This is commonly referred to as "bass management". 

The CORRECT signal to be sent to the center speaker is only the sound that's common to the left and right speakers. This doesn't minimize stage width. It's helpful for a little of that information to be sent to the left and right speakers to help create left of center and right of center images. 

Audiofrog's Multiseat Stereo, which is based on the Penteo upmixer and reworked a bit for automotive works this way. Center is only COMMON information. The sides and the rears are NOT a differential signal, so there are no annoying artifacts from the sides and the rears. Controls exist in the tuning panel to allow you to spread the intermediate (left of center and right of center) out toward the left and right and also toward the sides. Another set of controls allow you to spread the differential information (left only info and right only info) toward the sides and the rears. Used with some additional delay, this can create a better sense of width, depth and ambience. 

Since phase isn't used to extract the center and isn't used to split the stereo signal into intermediate and differential info, there's no frequency response coloration. The bass remains punchy and impactful. Setting the system up so it works in both front seats and the back seats too is much simpler than trying to do that with all pass filters. It's actually about as easy and about as straightforward as setting up a basic 2-channel stereo. No left and right delays are necessary and the frequency response between left and right doesn't have to be as precisely matched.

Yes, one of these days, it'll be available. We're working on hardware now. And yes, just like Julian's algorithm, it won't run on a basic DSP that you find in most processors. We're putting it on a SHARC.


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## Patrick Bateman (Sep 11, 2006)

seafish said:


> Your talking about ambio sound and IIRC one of the current oem "high end" sound systems IS using headrest mounted L+R speakers. But you are right, it is complicated to properly implement. Patrick Bateman has posted more then one thread about it.


If a couple million dollars showed up in my bank account I'd probably buy about three or four cars and I'd set up each one with a different system.

As Erin mentioned, the answer to your question largely depends on what you listen to. I know Jon Whitledge has taken a lot of flack because he controls his demos very carefully, but I think it's for a good reason:

_Some recordings sound great in stereo, but a lot don't._

For me, the recording that I really enjoy on a multichannel setup are the ones that don't have much of a soundstage. Basically the multichannel experience adds some ambience that's largely absent from the original recording. The Lexicon system in my Genesis does up-mixing from stereo to seven channel, and I listen in that mode 90% of the time.

So it's definitely a pleasant way to listen to music, but whether you will like it will largely depend on how well your music is recorded.

If I had limitless funds, I'd probably have a "stereo" car, a five channel car, a ambio car, a SPL car, etc...


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## Patrick Bateman (Sep 11, 2006)

jimmydee said:


> I've never been interested in doing a Center Channel... but I have always done Rear Fill.
> Just personal preference...
> 
> As SkizeR mentioned; it's a bit of an _'art form'_ to get rear fill to sound good.
> ...


That's been my experience too: a center channel is great if you have two or three people listening to the soundsystem.

But if you have the luxury of setting it up for one listener, you can get a wider stage with two speakers. Basically the center channel will 'drag' the soundstage toward the center. 

Rear speakers do that to an extent, but since their level is low it's not as big a problem.


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## Patrick Bateman (Sep 11, 2006)

durwood said:


> For rear-fill I would start with midbass only rear-fill. It will aide in fixing the lopsided azimuth angles and also help correct room mode nulls. It's a two-fer improvement. The car is a small room that pushes room modes into midbass territory. HT guys use multiple subs to fix room modes in medium to larger rooms, but our room is smaller.
> 
> It does work, I suggested to a friend to do in in his golf R simply using stock locations and he was surprised. I view him as someone who has tuning abilities and works with this stuff everyday beyond my rather hobbyist dabbling, so surprising him with this concept was cool. Gain and filter frequencies do have to be played with. He has also played with Hafler rear fill (L-R, delayed, gain) way back in the 90's, but he had never considered something simpler.
> 
> I believe werewolf once also suggested mid-bass arrays, and there was a thread here on it, but I don't remember it covering the room mode aspect of it. That is probably the main benefit, and fixing azimuth errors via vector summation is just a side benefit.


Interesting.

I've had a lot of luck with midbass arrays. Subjectively, they sound fantastic. Objectively, I wind up arguing with people, trying to explain why 2-4 small midbasses are superior to one large midbass. Your post here might explain it.

Subjectively, I've found that the use of multiple midbasses tends to make the lower frequencies sound 'diffuse.' When I've used a single midbass on each side, I've found that the soundstage is 'anchored' to wherever the midbass happens to be. The use of multiple midbasses seems to confuse the imaging cues, and winds up making the soundstage sound bigger than the confines of the car.

It's neat


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## Patrick Bateman (Sep 11, 2006)

GotFrogs said:


> Yes, one of these days, it'll be available. We're working on hardware now. And yes, just like Julian's algorithm, it won't run on a basic DSP that you find in most processors. We're putting it on a SHARC.


At this point I'm not sure if Penteo exists. I've heard it in Gary's car, I've heard you talk about it, but I can't buy it at any price.

ANDY TAKE MY MONEY PLEASE

Based on my previous interactions with Penteo, this post will not receive a response. I think Penteo is a unicorn.


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## 156546 (Feb 10, 2017)

Patrick Bateman said:


> At this point I'm not sure if Penteo exists. I've heard it in Gary's car, I've heard you talk about it, but I can't buy it at any price.
> 
> ANDY TAKE MY MONEY PLEASE
> 
> Based on my previous interactions with Penteo, this post will not receive a response. I think Penteo is a unicorn.


Well, we're working on the car audio version, but if you want it as a VST, you can buy it at perfectsurround.com.

Just click the "buy" button and your unicorn will appear.


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## 156546 (Feb 10, 2017)

And I'm pretty sure the Penteo guys aren't lurking around on DIYMobile waiting for you to call them out...


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## SkizeR (Apr 19, 2011)

Lol

Sent from my SM-G950U1 using Tapatalk


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## jerry236 (Jan 25, 2014)

wowza!!


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## FordEscape (Nov 23, 2014)

GotFrogs said:


> ... Matrix processors like Logic 7 and Dolby PL2 use a L+R center. To counteract the stage narrowing problem (to keep the stage as wide as possible), they use a steering matrix which calculates a "steering angle" and that calculation is fed to a bunch of automatic level controls that turn channels up and down really quickly. So, if a signal is steered to the center, the right and the left channels are attenuated. If a signal steers right, then the center and the left are attenuated.
> 
> Because the ENTIRE signal is turned up and down, these algorithms don't do a very good job of resolving the location of transient sounds while there's a steady state sound in the background. This causes steering errors. ....


These questions probably exposing my totally unsophisticated understanding of these matters, but so it goes ...

Andy, should I now understand that the MS8 L7 center is based on _not just_ the "mono" sounds in a recording (those sounds _common_ to both L&R), but _all_ L*+*R sounds with the added 'steering' treatment you described in an effort to minimize 'stage-narrowing'?

That's not what I'd understood from previous writings (and language in the MS8 manual on page 37) but hey, learning the nuances is fun.

Can you perhaps more fully explain the nuances of toggling the MS8 "Seat" setting between "Driver" and "Front" _when a center channel has been configured during setup_? For example, when "Driver" is selected does that negate the L7 'center processes' and very closely approximate the perhaps more desirable (from a stage-width perspective) 'without a center' configuration optimized for driver-only listening?

Or, as I suspect, is it only possible to achieve '_optimal_ driver only listening' by configuring the MS8 without the center 'from scratch' OR achieve ' _least compromised / most desirable_ multi-seat listening' by configuring the MS8 with center 'from scratch', with no way to 'toggle' between those two after a given IO configuration/setup/autotune is done?


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## 156546 (Feb 10, 2017)

FordEscape said:


> These questions probably exposing my totally unsophisticated understanding of these matters, but so it goes ...
> 
> Andy, should I now understand that the MS8 L7 center is based on _not just_ the "mono" sounds in a recording (those sounds _common_ to both L&R), but _all_ L*+*R sounds with the added 'steering' treatment you described in an effort to minimize 'stage-narrowing'?
> 
> ...


I used to describe the operation of L7 based on the net effect of the algorithm rather than on the ACTUAL operation. The net effect is that center is sent to the center and attenuated by about 6dB in the left and the right. In fact, this is how the adjustments are often made in the UI--similar to the "panorama" settings in other upmixers--that changes the automatic level control operation in order to place more or less of the center information in the left and right.

MS-8's auto setup routine automatically sets delay and EQ. The differences between driver, passenger and front change the delay and EQ settings based on averages over those seating positions. Choosing passenger reverses the delay settings. Choosing center eliminates the left and right delay and leaves the delay used for matching drivers at crossover points for a center placed mic (this is determined from the driver and passenger measurement routines). The benefit in optimizing for the driver over the "front" is in one area only--and that is the placement of midbass sounds below the center speaker high pass filter. In "driver" or "passenger" the correct placement is ensured using delays, just like in a stereo system. In front, you'll likely experience a near side bias of midbass below the center high pass filter. 

Our new upmixer, which we're now compiling for a SHARC to go in some hardware uses a different method for fixing the near side bias below the center high pass. It works great and provides an improvement in both seats. After reviewing a lot of prior art, we've applied for a patent for the combination of that solution with a particular type of upmixer.


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## FordEscape (Nov 23, 2014)

GotFrogs said:


> I used to describe the operation of L7 based on the net effect of the algorithm rather than on the ACTUAL operation. The net effect is that center is sent to the center and attenuated by about 6dB in the left and the right. In fact, this is how the adjustments are often made in the UI--similar to the "panorama" settings in other upmixers--that changes the automatic level control operation in order to place more or less of the center information in the left and right.
> 
> MS-8's auto setup routine automatically sets delay and EQ. The differences between driver, passenger and front change the delay and EQ settings based on averages over those seating positions. Choosing passenger reverses the delay settings. Choosing center eliminates the left and right delay and leaves the delay used for matching drivers at crossover points for a center placed mic (this is determined from the driver and passenger measurement routines). The benefit in optimizing for the driver over the "front" is in one area only--and that is the placement of midbass sounds below the center speaker high pass filter. In "driver" or "passenger" the correct placement is ensured using delays, just like in a stereo system. In front, you'll likely experience a near side bias of midbass below the center high pass filter.
> 
> Our new upmixer, which we're now compiling for a SHARC to go in some hardware uses a different method for fixing the near side bias below the center high pass. It works great and provides an improvement in both seats. After reviewing a lot of prior art, we've applied for a patent for the combination of that solution with a particular type of upmixer.


Thank you, Good Sir, for the always appreciated continuing education. You've helped me better understand why I've sometimes struggled to judge whether I'm 'better or worse-off' with my MS8 center-channel experiments. I do love my MS8 but sometimes need reminding that it's not realistic to expect a single solution to be _optimal_ for all situations and that so much does depend on the individual recordings.

Not sure I'll be able to avail myself of it but I've no doubt that your continued efforts in developing technology to better improve car audio will be fruitful. I'm glad that the industry has you, and feel fortunate that you choose and are able to share your insights with 'laypersons' such as myself so capably. Thank You.


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## Patrick Bateman (Sep 11, 2006)

GotFrogs said:


> Well, we're working on the car audio version, but if you want it as a VST, you can buy it at perfectsurround.com.
> 
> Just click the "buy" button and your unicorn will appear.


I guess you could do it like this:

1) buy Penteo VST plugin

2) Process your library on a laptop or desktop

3) encode the files as five channel AAC

4) Play them back using a Windows tablet with a USB sound card

I'm not sure if it would be possible to process them in real time with Penteo in the car, because Windows tablets are quite slow. Obviously, you could buy a Surface or something similar, but I'm not too keen on leaving a $1000 tablet hooked up in my car 24x7. With the cheap Windows tablets you can hide them fairly easy.


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## 156546 (Feb 10, 2017)

Or you could get a mini PC. I used to do spatial processing in a mac mini I used as a head unit. It's now my LEAP PC because it's the last thing I have that runs XP.


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## fullergoku (Jun 21, 2009)

Andy is there any chance you will release your improvements on the penteo software that you will be using in your processor as vst plugin?


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