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Hardware Thread, Combining Audio Inputs in Technical; ...
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    enjay's Avatar
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    Combining Audio Inputs

    I'm trying to get the audio feed from a PC and a DVD player into one set of speakers without having to buy £60 dual-input speakers. So, I bought the necessary converter cables, BUT... the sound from either of the devices is almost inaudible while both other are connected, but fine if they are on their own. I have other 2-into-1 PC audio adapters which work fine, so I'm wondering if the problem is my RCA-to-3.5mini converter.

    Other than giving up and buying the £60 speakers, has anyone got any suggestions? Might I have more luck if I bought speakers with RCA inputs on them and converted the PC signal than the other way around? Whatever solution I find will need to be done to quite a few computers, so needs to be as cheap as possible.

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    Domino's Avatar
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    hmmm, have you tried a little pre-amp or similar to boost the signal before sending it to the speakers?

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    mattx's Avatar
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    Sounds a bit daft but won't a simple audio switch do ?

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    The way I did it was to connect the output from the DVD player in to the Line-In on the PC and the PC's Line-Out to the speakers. You can then use the volume control on the PC to control the DVD level, it might not be perfect but it's cheap!

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    enjay's Avatar
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    Quote Originally Posted by mattx View Post
    Sounds a bit daft but won't a simple audio switch do ?
    Possibly; ideally I'd like something passive though, as I suspect I would quickly get sick of people saying "the DVD player is broken" when they just needed to flick the switch. It is hard enough getting some people to learn how to re-scan the projector to the video input without adding another step to the proceedings!

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    enjay's Avatar
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    @rhyds - is that using a fancy soundcard or just the regular mic in port on the PC?

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    Quote Originally Posted by NickJones View Post
    Possibly; ideally I'd like something passive though, as I suspect I would quickly get sick of people saying "the DVD player is broken" when they just needed to flick the switch. It is hard enough getting some people to learn how to re-scan the projector to the video input without adding another step to the proceedings!
    Thats true, I setup audio switches on all our PCs / DVD / TVs in our classrooms - in the end I ended up putting VERY LARGE STICKERS on them stating which switch did what and how to use it, what a volume control actually does and how leaving the volume control right up on the speakers is not a good idea....

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    The problem is that there is slight power coming from any PC sound card/on-board. If you are playing a DVD on the separate player if you turn the PC of the sound will be ok! That is how we got around it.

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    Quote Originally Posted by NickJones View Post
    @rhyds - is that using a fancy soundcard or just the regular mic in port on the PC?
    Regular onboard HP soundcard. I used the line-in rather than the mic input and used the windows volume control to set the levels etc. right

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    Your problem is an impedance mis-match. The output of the DVD will be something like 10k ohm, but the PC is 600 Ohm. This results in the PC sinking the voltage that should be going to the speakers.

    You can use a matrix of resistors to get over this problem, or a variable resistor. I can look up the values I used (if I can find the scrap of paper...)

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    can't find what I mean on maplins ( and however I do agree with the amp before connecting to speakers ) but just as a thought.

    Not sure what they are called but will try and explain anywho ( these type of things )

    http://www.tlc-direct.co.uk/Images/P..._3/TLCON15.JPG

    those electrical block things where you get a screw driver and it has copper inside and you take a wire in at each end and screw the wires in at each end and it connects the wires together and then you use electrical tape around them

    If you take the left wire from the left audio output from the dvd player and the same again from the pc and screw that in one end and do the same for the right side audio cable and then connect both speaker cables into it to combine it .

    will have a look later on ( probably sounds like a bunch of cr4p at the min lol )

    Gotta run for now though

    you will have to chop the wires for the speakers and the dvd and pc outputs but will use the above to re connect them that way you dont have to use a switch but obviously if they try and use both together it will most likely distort.
    Last edited by mac_shinobi; 6th February 2008 at 04:18 PM.

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    Quote Originally Posted by NickJones View Post
    Possibly; ideally I'd like something passive though, as I suspect I would quickly get sick of people saying "the DVD player is broken" when they just needed to flick the switch. It is hard enough getting some people to learn how to re-scan the projector to the video input without adding another step to the proceedings!
    Yes you do, it gets old very quickly.

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    Not sure what they are called but will try and explain anywho ( these type of things )
    I call them choc boxes

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    mac_shinobi's Avatar
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    hhmmm

    Quote Originally Posted by mattx View Post
    I call them choc boxes
    thats what I thought but when I came to search for them it took me a while to get that image and I still can't find it on maplins or else where - unless im just being a numpty like I usually am when it comes to finding stuff on sites like dabs and misco etc.

    would be nice to know the official name

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    We do the same as rhyds, push all the audio through the PC at line level. It's the best solution we found, totally transparent to the user (as long as the PC's switched on!). Make sure you connect the DVD to line in (blue) not mic in (pink) or you'll blow up the sound card in the PC.

    Chocblock will still give you the impedence problems, ie all the PC being greedy and absorbing the DVD's audio before it reaches the speakers.

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