# Computer for head unit



## audiophiledave (Nov 8, 2009)

I am tinkering with the idea to build a computer for the use as a head unit and full equalizer tunning. I have used the search option but everything is scattered, I am just wondering how the process would work. Computer straight to amplifiers? or computer to a processor to amplifiers?


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## frmdrkside (Jul 13, 2008)

If you haven't already checked it out mp3car.com is the best forum for in car cpu info IMHO.

As far as your question, you could sort of do it either way. With the cpu to amplifier, you'll have to shell out a little money for a nice sound card, but you can do all your processing from the cpu. You'll need to be sure you have ample cpu resources though. You may also consider a line driver, depending on what sound card you go with.

Personally I kind of like the cpu to processor to amplifiers approach, utilizing digital out of the cpu to a processor then to amplifiers. With this design the cpu is simply a digital source and the processor provides all tuning control and d/a conversion. You just need a processor with a digital input (toslink, AES, ect.) and a digital out on the cpu. You also can go more conservative on the cpu power since it doesn't have to provide the processing resources.

Hope that's helpfull.


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## audiophiledave (Nov 8, 2009)

frmdrkside said:


> If you haven't already checked it out mp3car.com is the best forum for in car cpu info IMHO.
> 
> As far as your question, you could sort of do it either way. With the cpu to amplifier, you'll have to shell out a little money for a nice sound card, but you can do all your processing from the cpu. You'll need to be sure you have ample cpu resources though. You may also consider a line driver, depending on what sound card you go with.
> 
> ...


Hmm very tempted, just out of curiosity I have a 3sixty.2 laying around but never used it, can you enter the specific frequency you want to adjust or is it pre-assigned, and if you can't do you know of any processors that allow you to do that?


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## MarkZ (Dec 5, 2005)

I use mine to do all the processing. It can be a little tricky to set up though. mp3car has a couple of nice guides written on the subject by durwood. I wrote a guide in the tutorials section of this forum about using foobar2000 and plugins to do the processing, which is a lot easier IMO.

You need to start out by selecting a good user interface. Touchscreen, where to mount it, remote controls, usb volume knobs, steering wheel control interfaces, etc. This is 90% of the battle of using a PC in the car. But mp3car sells all this stuff. Next, you choose a sound card. Determine how many output channels you need, ... PCI, USB, firewire? Then you determine what kind of software you want to use. People use "front ends" like road runner to provide a better user interface for touchscreens. I don't. 

Finally, after you choose all those things, you shop for hardware. You need a power supply that works in the car (eg. m1-atx, carnetix, etc), you need a motherboard/memory/hard drive that's capable of running the processor. And perhaps most of all, you need to be conscious of temperatures... computers don't like hot and they don't like extreme colds. So make sure it gets adequate ventilation, make sure you use efficient hardware (eg. the "green" 45w CPUs). Cold weather problems start to crop up at around freezing temperatures. Many AMD cpus don't work below about 30 degrees ("cold bugged"), and I've found that hard drives don't like to spin up below about 17 degrees (IME Seagate does better than Maxtor and WD at this).

Good luck!


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## audiophiledave (Nov 8, 2009)

MarkZ said:


> I use mine to do all the processing. It can be a little tricky to set up though. mp3car has a couple of nice guides written on the subject by durwood. I wrote a guide in the tutorials section of this forum about using foobar2000 and plugins to do the processing, which is a lot easier IMO.
> 
> You need to start out by selecting a good user interface. Touchscreen, where to mount it, remote controls, usb volume knobs, steering wheel control interfaces, etc. This is 90% of the battle of using a PC in the car. But mp3car sells all this stuff. Next, you choose a sound card. Determine how many output channels you need, ... PCI, USB, firewire? Then you determine what kind of software you want to use. People use "front ends" like road runner to provide a better user interface for touchscreens. I don't.
> 
> ...


I been building computers for five years and have built probably 30+ computers so I I understand everything coming from the computing side. What I would like to do is go straight rca from the sound card right into a line driver to the amps, and maybe once I get some additional money to buy an audison bit one in order to retain the digital signal. Do you find it easier to tune your system with the plugins and do you get a better end result then using a normal processor or head unit?


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## MarkZ (Dec 5, 2005)

Well, I've been doing carPCs for about 10 years now, so I don't really have much first hand experience with head units. Last head unit I used was a Nak CD45z. It had no processing. 

I was using a pair of Behringer DCX2496's to do processing a couple years back. The CarPC has way more features.

If you check out my build log you can see some of the software tuning I've done in my install. I don't know what the bit one does that you think a carPC can't. Go to this site and check out some great multichannel plugins. Pay particular attention to the GlissEQ, CurveEQ, Sound Delay, and LF Max Punch. There are also limiters and compressors and stuff that could be useful.

There are also many other companies and individuals that make useful VST plugins, some of which are free.


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## t3sn4f2 (Jan 3, 2007)

http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/59143-help-me-design-carputer-take-down-bit-one-dsp-6-a.html


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## frmdrkside (Jul 13, 2008)

audiophiledave said:


> Hmm very tempted, just out of curiosity I have a 3sixty.2 laying around but never used it, can you enter the specific frequency you want to adjust or is it pre-assigned, and if you can't do you know of any processors that allow you to do that?


3sixty.2 doesn't do digital input, and if your not doing digital out of the cpu then there's no point in doing an external processor. The cpu is capable of more processing options than most any external processor. I'm not 100% sure but I think the bit one offers ferquency selections in it's parametric eq's. Most any pro audio processor will allow for that, Rane RPM, EV DC-One, ect. They all have digital AES input, but need to be converted for 12v operation.

MarkZ has given alot of good advice in this thread, and I agree with all of it. The processing capability of a car pc is really only limited by the cpu resources you have available. As I said though, I like the digital out to a processor, but that is more for simplicities sake. I also think that it is a little cheaper to go the digital to processor route, but there's alot of varibles that could swing it either way. If your willing to do the research you can pretty much do anything with a car pc.


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## t3sn4f2 (Jan 3, 2007)

frmdrkside said:


> *3sixty.2 doesn't do digital input, and if your not doing digital out of the cpu then there's no point in doing an external processor.* The cpu is capable of more processing options than most any external processor. I'm not 100% sure but I think the bit one offers ferquency selections in it's parametric eq's. Most any pro audio processor will allow for that, Rane RPM, EV DC-One, ect. They all have digital AES input, but need to be converted for 12v operation.
> 
> MarkZ has given alot of good advice in this thread, and I agree with all of it. The processing capability of a car pc is really only limited by the cpu resources you have available. As I said though, I like the digital out to a processor, but that is more for simplicities sake. I also think that it is a little cheaper to go the digital to processor route, but there's alot of varibles that could swing it either way. If your willing to do the research you can pretty much do anything with a car pc.


Sure there is. When you want the same sound quality as digital plus you _want_ to use a processor that doesn't have digital input. Some reasons to want that would be simplification yet great sound, and processing options that a carpc can't give you (MS-8 Logic7).


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## frmdrkside (Jul 13, 2008)

t3sn4f2 said:


> Sure there is. When you want the same sound quality as digital plus you _want_ to use a processor that doesn't have digital input. Some reasons to want that would be simplification yet great sound, and processing options that a carpc can't give you (MS-8 Logic7).


You lost me here a little bit. The material on the cpu starts in the digital format. The cpu sound card is doing the d/a conversion then analog (preamp) out to the processor, the processor is doing an a/d conversion, processing the material in a digital format, then d/a conversion again, then analog (preamp) out to the amplifiers. Add in the possible need for a line driver between the cpu and the processor and you end up with a pretty complicated signal path. Certainly not simplified, and it isn't any better than just using a good (non digital out) headunit. I guess to me it seems like a bit of a waste. Go with the cpu resources that allow it to handle the processing, keep the material in the digital format, process it, then do the d/a conversion once (you also completely eliminate the a/d conversion). This idea is the same if your using a processor with digital in. The processor becomes your d/a converter and you can go with a fairly low resource cpu setup. Most of the mini itx boards come with toslink built on.

You are right though, and I stand corrected, that the MS-8 is offering some stuff that you can't get in any other processor, the logic 7 and also the Autotune function(alpine imprint does this also but I don't think it can be used stand alone). Since it doesn't do digital in, if you want those features you don't have much choice.


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## t3sn4f2 (Jan 3, 2007)

frmdrkside said:


> *You lost me here a little bit. The material on the cpu starts in the digital format. The cpu sound card is doing the d/a conversion then analog (preamp) out to the processor, the processor is doing an a/d conversion, processing the material in a digital format, then d/a conversion again, then analog (preamp) out to the amplifiers. Add in the possible need for a line driver between the cpu and the processor and you end up with a pretty complicated signal path. Certainly not simplified, and it isn't any better than just using a good (non digital out) headunit. I guess to me it seems like a bit of a waste. Go with the cpu resources that allow it to handle the processing, keep the material in the digital format, process it, then do the d/a conversion once (you also completely eliminate the a/d conversion). This idea is the same if your using a processor with digital in. The processor becomes your d/a converter and you can go with a fairly low resource cpu setup. Most of the mini itx boards come with toslink built on.*
> You are right though, and I stand corrected, that the MS-8 is offering some stuff that you can't get in any other processor, the logic 7 and also the Autotune function(alpine imprint does this also but I don't think it can be used stand alone). Since it doesn't do digital in, if you want those features you don't have much choice.


Yup, the digital out from the source or the d/a to the line driver or whatever directly from the PC (when it is doing the processing) eliminates an d/a-a/d, but here's all that is lost in those two extra conversions _if done correctly_ and decent affordable gear is used.

Below is the measured difference between a digital output (they all measure the same, nothing out there is better or different for that matter) and the analog output of a soundcard. Included are the results for both the analog and digital domain of a CD format (ie 16bit/44kHz) and a high resolution format (24bit/44kHz). These results are indicative of what we are talking above because the software that is doing the analysis sends the digital test file from the pc to the d/a of the soundcard and then that analog signal goes back into the a/d of the soundcard. Essentially it measures that part of the chain only and the degradation caused the d/a-a/d. The card that was measured is a bottom of the line EMU PCI card that is under $100.


Summary:










Frequency Response:










Noise:










Dynamic Range:










THD:










IMD:









Crosstalk:









Swept IMD:










You can see by the reduced performance of the CD resolution that the limiting factor in a modern converter is not the conversion itself but the format being played. And we know the CD format is good enough for everyone except test instruments.


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## MarkZ (Dec 5, 2005)

frmdrkside said:


> You are right though, and I stand corrected, that the MS-8 is offering some stuff that you can't get in any other processor, the logic 7 and also the Autotune function(alpine imprint does this also but I don't think it can be used stand alone). Since it doesn't do digital in, if you want those features you don't have much choice.


It's worth pointing out that carPCs and the appropriate VST plugins can do a LOT of things that the ms8 can't do, also. For example, LFE enhancement, phase adjustment, compressors and limiters, custom channel mixing, frequency band-specific processing, FIR filtering, and ultimately more bands of EQ (though I don't know why you'd need that many...). The MS8 was designed to be a drop in processor, and it appears to be an amazing product, but it's not as customizable as VST plugins.

I'd like to see someone develop a box that loads VST plugins. You hook your laptop up to it, change things around like in Console or Audiomulch, and then it acts as your processor. Basically doing what the computer does, but without the OS.


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## audiophiledave (Nov 8, 2009)

t3sn4f2 said:


> Yup, the digital out from the source or the d/a to the line driver or whatever directly from the PC (when it is doing the processing) eliminates an d/a-a/d, but here's all that is lost in those two extra conversions _if done correctly_ and decent affordable gear is used.
> 
> Below is the measured difference between a digital output (they all measure the same, nothing out there is better or different for that matter) and the analog output of a soundcard. Included are the results for both the analog and digital domain of a CD format (ie 16bit/44kHz) and a high resolution format (24bit/44kHz). These results are indicative of what we are talking above because the software that is doing the analysis sends the digital test file from the pc to the d/a of the soundcard and then that analog signal goes back into the a/d of the soundcard. Essentially it measures that part of the chain only and the degradation caused the d/a-a/d. The card that was measured is a bottom of the line EMU PCI card that is under $100.
> 
> ...


I know this is a noob question but what does THD and IMD stand for as well as cross talk?


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## t3sn4f2 (Jan 3, 2007)

audiophiledave said:


> I know this is a noob question but what does THD and IMD stand for as well as cross talk?


Audio system measurements - Wikipedia, the free encyclopedia


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## audiophiledave (Nov 8, 2009)

t3sn4f2 said:


> Audio system measurements - Wikipedia, the free encyclopedia


Now I feel like a dumbass lol... it seems analog still has its advantages over a digital signal and that the distortion levels are still low enough to not make a big enough difference.


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## frmdrkside (Jul 13, 2008)

t3sn4f2 said:


> You can see by the reduced performance of the CD resolution that the limiting factor in a modern converter is not the conversion itself but the format being played. And we know the CD format is good enough for everyone except test instruments.


I don't think I stated or implyed that an analog output from the sound card or the additional a/d or d/a conversions in the signal path would produce inferior sound quality. In fact I said it would be the same as using a high quality (non digital) headunit. I did say that it didn't simplifiy things, and I believe that is correct. The other issue not addressed, is car audio specific noise. Digital signal transfer between devices eliminates the possibility of radiated noise and ground loops, and IMHO is better in the vehicle enviroment for that reason alone.

I try and keep things simple, guess my perspective is why do it if you don't have too. As I said, I don't see the point in going non digital to a processor, when at that point you can save your money on the processor all together. Spend a little more on a more powerfull cpu, nice soundcard, line driver and get the same or more processing capability. Conversely, you can go with a less expensive cpu setup, use built on toslink out, to processor and the processor does your processing and high volt preamp. I don't get buying a less expensive cpu, nice soundcard, line driver, to run to a processor that does processing and high volt preamp. It just seems redundant to me. Except, in the situation that I conceaded to you with the MS-8 and it's unique feature set. 

Maybe it'd be more clear like this.

Option #1
Powerful CPU
Nice sound card
Linedriver

Option #2
Standard CPU
Processor

Option #3
Standard CPU
Nice sound card
Linedriver
Processor

With option #3 you have to have everything from option #1 & #2. I guess that's my main issue with it. Not a very streamline approach. You could eliminate the sound card from option #1 & 3 and the need for a processor with digital input from option #2, if you used built on preamp audio, but personally I would never do that. Bottom line though is any of the 3 configurations will probably work well.

To OP, figure out your needs, do some research, and take the route that will be easiest on your wallet.


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## MarkZ (Dec 5, 2005)

Option #4
Standard CPU
Nice sound card
No external processor

Audio processing doesn't necessarily have to be terribly CPU-intensive. Most people use CPU-intensive VST plugins for some reason. If you use a VST host inside the player (available to both foobar2000 and winamp), and use good VSTs, you can make it work without having to get exotic with your CPU. I use a simple dual core AMD duron (2.1GHz I think?). 8 channels of processing -- bandpass crossovers/EQ with 4x oversampling + delay + channel mixing -- and my CPU usage still doesn't exceed 20%.


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## frmdrkside (Jul 13, 2008)

MarkZ said:


> Option #4
> Standard CPU
> Nice sound card
> No external processor
> ...


I'm talking standard cpu being a VIA C7 1.5 ghz or Intel Atom 1.6 ghz. I'd say a 2.1ghz AMD Duron dual core is pretty big for the car enviroment. Good lord, it's bigger than my current desktop!! Are you using a mini itx motherboard? If so which one? and how much RAM? Are you using a line driver?

According to my standards your option #1.


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## MarkZ (Dec 5, 2005)

Haha I figured by today's standards dual core was old school.

Anyway, it's a small board about the size of a mini ITX. I pulled it out of one of these:

Acer Aspire Athlon 64 X2 4000+ 1GB 250GB DVD±RW Vista Acer ASL100-UD400A

Then I replaced the CPU with an energy efficient sempron (I think) that was a little slower but dissipated about 40% of the power (_very_ important in a car).

I think I've got 1GB in it. And no, I'm not using a line driver.


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## Stage-Auto (Jul 14, 2010)

so when's it going in?


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