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  • Control Gain on Digital output through Computer

    Can you control the gain (volume) of a digital signal (S/PDIF) through the volume control on the computer i.e. media engine or mediacar volume control
    -Jesus- King of Kings Lord of Lords

  • #2
    I have been researching this a lot lately. The answer is no. Digital output is a 'set' level. Only the decoding device (DSP, DAC, home stereo [there are no digital inputs that I could find in car stereo]) can change the volume (gain), after it is decoded.

    HTH!

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    • #3
      Thanks for the response. I figured as such. What about an aplication that will run on the PC that could do that. It sounds like it needs to be done in software if the protocol can carrie the information

      Check out the Panasonic CY-AC300 and Apline PXA-h510 and PXA-H700

      These both have toslink inputs
      -Jesus- King of Kings Lord of Lords

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      • #4
        looked at those. Thanks for the info.

        unfortunately those are DSP's. For my particular setup, I wanted to use the optical output from my carpc to go into my head unit, strictly to isolate any background noise the computer might introduce into the audio. I did not really have any interest in running 5.1 or similar processing.

        So that puts me in a bit of a quandry. The only way to implement the isolation I want requires me to buy a DSP. But a DSP is a lot of money to spend just for some isolation. I know I could buy a DAC, but again, kind of silly and expensive just for this purpose.

        I am to the point where I have decided that I will probably just use a USB sound card, and hope that reduces background noise sufficiently; unless I can find a better alternative.

        As for your idea: I think you are saying that you want to use the PC to 'control' your DSP. I don't think that option is available. The optical in only carries audio, my understanding. BUT, I do know that many DSP's offer remote control. So you could place the DSP somewhere hidden and operate it via the remote. Unfortunately though since you can't see the display, it is somewhat difficult to make real use of the DSP at that point.

        You will have to let me know if you know or find out otherwise, because I really had hoped to do pretty much what you are doing, until I found all of this out today.

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        • #5
          First off read this thread if you havn't already. It is the hurtles that i have crossed along the way to getting dolby digital 5.1 http://www.mp3car.com/vbulletin/showthread.php?t=24884

          It may help and may not.

          Sounds like you are on a budget so a DSP sounds out of the question and sounds like you are not interested in dolby digital or dts so that really makes a DSP out of the question.

          If all you are after is no ground noise there are many threads that are available through a search that will tell you tips and tricks on reducing ground loops. I wanted to go digital to avoid all of that and i also wanted true 5.1 dolby digital and dts so my only choice was to get a dsp. No sound card offered all of that.

          Are you sure that there is no Head units that take Optical or Coax for inputs? or even a seperate convertion unit that has an analog out and digital inputs so atleast you could run the digital signal most of the way and have the analog signal only travel a very short distance.

          For my scenerio i am not really interested in having the PC control the DSP....only the gain. I was thinking that while the signal was digital that it had to have a gain. If this is true then you could control the gain of the digital signal with software.

          I will have to do some research on this. It's not such an issue becasue it wont kill me to adjust the volume on the DSP's control unit.

          Good brainstorming with you

          Cheers
          -Jesus- King of Kings Lord of Lords

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          • #6
            TY for the advice. This does give me some ideas, but it is more and more obvious that seeking digital sound without 5.1 is really not possible without paying the expense of 5.1. In other words, probably not worth it in cost/gain.

            Main goal is not neccesarily ground noise, but the various pops, hums, and etc that come up in a PC when you put in a CD, access things, etc. I really need to start putting it together and testing before I make any expensive decisions. I just knew this would solve it, and hoped it would be easy, IE a digital in on a head unit. But never was able to find one. If in your research you do, please do me the favor of dropping me a PM about it. Thanks for all the thoughts.

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            • #7
              This whole endevour (5.1 surround sound) has been one huge learning experience with a lot of trial and error.
              -Jesus- King of Kings Lord of Lords

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              • #8
                If your DSP comes with a remote, you can use a USB IrDA to control the volume via PC. Mount the emitter somewhere within line-of-sight of the DSP control, and where it wont be likely to be blocked. Or, if you don't need your DSP visible, you can just mount them somewhere hidden away so there's no chance of blocking the signal.

                For those without a remote... you could open up the DSP's casing and solder on wires to the volume Up/Down buttons... and control them via Com port. Even if you want the DSP screen visible, you can still solder on the wires inside and run them to the PC with no problem. That way, DSP is still nice and pretty, and you can control volume via PC or with the buttons on the DSP.

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                • #9
                  Thanks for the helpful information.

                  I guess that the goal is to be able to control the digital sound with mediacar. I could feasabily do the IRDA route except that the DSP's control unit does not have an remote.

                  Hacking up the DSP is kindof out of the question because I can't program so even if i get to the point where I get the sodering done and wires coming out into a serial cable i would then have to write a little progrma that will have MediaCar or whatever front end control the volume.

                  It would probably be easier to get the code written myself than getting the creators of the front end to add it in to the native code
                  -Jesus- King of Kings Lord of Lords

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                  • #10
                    Oh yeah, deffinitely. You can find tutorials out there on maniuplating the COM port. It's not that hard at all to do in VB.

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                    • #11
                      forgive my ignorance here...

                      If you wanted to control switching with your com port, wouldn't you need some kind of a PLC (programmable logic controller) to sense the com port signals and switch things on and off? How tough would it be to customize this? I know it might seem easy to someone in the know, but to a newbie like me, it seems difficult.

                      I am actually pretty interested in trying something like this for my Air conditioning controller is why I ask. In my particular car (corvette) the A/C controller receives compressor pressures on the high and low side, and computes cycling of the compressor. I therefore cannot simply remove my AC controller from the dash, since I need its 'brain' to compute that. BUT... With the type of controller you mention, I could hard wire to the switches on the AC controller itself, and just send signals to simulate somone pushing the buttons to adjust the fan, temp, etc...

                      Seems like a good ide except what if the computer is down, I would be out AC control. Hmm... I can maybe work around that, but I am putting the cart before the horse here. Hoping you see this Banderon and give me some ideas!

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                      • #12
                        i use SPDIF out and its controled via the windows volume
                        Pete Kastner www.KastNERD.com

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                        • #13
                          Same here, on home pc used to use my sound card's optical output to record to minidiscs and able to change volume through sound card's volume adjustment software. Although, to optical output volume in general is not adjustable stand alone dvd and cd players
                          dk

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                          • #14
                            Okay, Okay.... Post your hardware setups that you got windows controlled SPIDIF Sound working.

                            Apparently I can controll the volume of MP3's and Videos (anything that is interprited as Linear PCM) but when it recieves a DD (Dolby Digital) Signal i must use the Gain Control on the head/control unite of my DSP
                            -Jesus- King of Kings Lord of Lords

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