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Car PC Audio Design

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  • Car PC Audio Design


    I'm in the process of designing software for my 350Z. I have a handle on everything on the software side of things... but having never been an audiophile (at least not with my cars) I'm a little unsure about my best audio setup.

    First of all I'm getting rid of the factory HU (the Z's system's all suck.. even the Bose upgrade) and getting a new one and an amp and probably some speakers. (I would love suggestions as I am not up on the market) So with this in mind.. I can purchase anything that will assist in the integration of PC to stereo.

    The software I'm designing is pretty responsive... I'm going to implement that with TTS from Festival. The problem is that when I'm driving at 110 with NoFX blaring I'm not going to notice the LCD when it's telling me that the ECU has something to ***** about. I need software control of all audio components. Not knowing much about car audio.. this is the solution I have planned:

    MIC -------------\ (mic)
    HU (Preamp out) --> (line in) PC (Integrated SC (VIA)) (lineout) --> AMP

    So I find a head unit with preamp out... turn the RCA into mini and back to RCA to go into the amp's preamp in (or to a crossover I guess). Then in software when I need to "say" an alert, I'd fade the Line to about 25% of the former volume and let the PCM channel go full on until the PC was done talking.

    My unknowns are what the impedance mismatch will be between the preamp out on the head unit and what the line-in expects, although I have a feeling that that will be less harsh than the amped (by soundcard) out into the amp. Also, I do care about fidelity and want to get the most out of the head unit I get. How much will going from RCA to mini to RCA cost in terms of quality? Is there another way?

    Any input is appriciated!


  • #2
    you can buy a car stereo that has a mute wire usually works on ground


    • #3
      I have done what you are talking about & it can be done without a problem*, basically there will be no impedance mismatch as the determining factor at line level is going to be more concerned with voltage. Use good quality connections & avoid using a 10' cable bunched up to do a 18" job & you'll be fine. You would adjust your head units volume initially & then not use it again, using your pc volume control instead. this way you will always have the volume levels in sync. with each other. keep in mind that the amp input is fixed, and if you adjusted the head unit volume directly, the pc wouldn't know how low or high the input to it is, & if you set the pc to say 3/4 volume & then turn down the head, you'd wind up listening to something low & then have your interupt blast louder, if you know what I mean.

      *now while you can do it that way & I have done it sucessfully In my last system that way, I would not recommend this as the BEST way for a few GOOD reasons:

      1)the head unit is the most convienient way to controll the overall system volume, this way sacrifices that,

      2) not to mention the "what if the computer is off,crashed,virused, or some other way temporarily bugged, it would be nice to not have it between your never fail head & amp

      3)the analog to digital & back to analog that the head signal goes through adds to degraded quality & if you want maximum sound quality, that's not it.

      there are a few others, but you get the idea.

      If you absolutely must have your audio interupt, then you can choose to just do it that way & it will be pretty good, maybe that would be enough for you, & maybe that's what you want.

      The better way to actually run a head unit with a pc is to use the pc as an aux input to the head. This will allow the head to control the volume of everything, including the pc. now while it is possible to still perform your interupts it would be more complicated. Some head units have a phone mute that you could activate easily enough with a few electronics,& then you could introduce your alert to either just the front speakers or all by mixing the signals at the input of the amps, but you would then have the same problem of the two volumes being independent.

      I actually got my system to work pefectly & the volume always stays in the same relationship to each other buy using the navigation mute input along with the guide control input on my alpine unit, but these inputs are only available on a multimedia head unit with it's own screen, althought that's what I did I doub't you'd want to add another screen to your mix.

      the final thought I'd like to share with you is that even after I got my whole thing working perfectly, it actually proved to be annoying to me to have my audio volume be interupted & I finally settled on a seperate speaker to feed me alerts that I could turn up enough to be authorative when I'm concerned about the alerts & turn it down to just a background wisper or even off when I'm not as concerned, all the while audible when necissary & not constanly mute/raise mute/raise, I'm much happier with it this way, but that's just me. If you used a small driver on say a pillar or somewhere close to your head, you can have it work where it is information for you, & not a total take over of the car each time as it would be the other way. I have this aux information subsystem that is comprised of my alerts, along with the cell phone & the onstar all coming out of a small (2x 2.5" drivers) aux speaker aimed at my ear, I've had it the other way & working fine with it muting the radio to about 25% & it proved more annoying than the way I have it now, & if I realized this from the begining I would have saved myself a lot of unecissary work.

      I don't know if any of my input here makes any sense to you & your install, but I hope I helped even a little....
      MY NEWEST INSTALL:modded infiniti fx with big screen

      first windows carpc liquid cooled LVDS screen :D


      • #4
        Thanks for the detailed post. Quite helpful.

        As for these muting inputs... what kind of signal do they expect? Do I Basic Stamp it or is it easier? Are there any head units with an electronic interface to switch inputs? Aux sounds ok.. but I don't want to press a button at the HU every time I want to hear the computer. Also.. doesn't anyone ever want to rock out a little while they're being told directions? I guess thinking about it... once I get my PC in.. I'll probably be playing mp3's all the time anyway.. so maybe it's a non-issue.

        Next hurdle: Automated talking blow-up doll for when I get pulled in the High Occupancy lane.


        • #5
          That's exactly my point, when you want to "rock out a little" it is extremely annoying to have it rudely interupted by directions. make believe you have a pasenger giving you directions, would you rather have them just speak up so you can hear them, or reach over & crank the volume down each time they want to tell you to "stay on the current road for 5.6 miles" while your jammin' tunes, if they constantly went up & down with the volume It gets ANNOYING real quick...

          the mute the head unit expects is a ground signal, what ever method you use to provide that should work, if you had any sort of other trigger than a ground, you should be able to use a relay or even devise a solid state circuit, I don't know much about basic stamps, but if you do I'm sure that could work to.

          as far as the blow up doll, that has crossed my mind to, I used to prop my gym bag up & actually throw a wig over the top, with tinted windows it was kinda an illussion enough to fool the casual observer, & at a toll I would just pull the wig down, but I got pulled over one day & got several tickets, including one labeled something to the effect of ".....malicious attempt..." don't remember the exct wording, but let me tell you, the officer was ****ed so much that among other tickets he gave me an individual ticket for each side window tinted as well as the rear & even the 4" strip of tint at the top of the windshield! the only tickets I beat were the tint ones & ate all the rest. needless to say I don't pull that stunt anymore....
          MY NEWEST INSTALL:modded infiniti fx with big screen

          first windows carpc liquid cooled LVDS screen :D