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Thread: can a carputer compete with a head unit for sound quality?

  1. #151
    Variable Bitrate fonseca's Avatar
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    Quote Originally Posted by JasonWW
    Why would you say that? The common, basic RCA cable is a 75ohm cable. We all use them and they work well for a digital signal as well. I use a cheap RCA cable for the digital coaxial out of my DVD and HD tuner to my reciever. Works like a charm. Maybe your hung up on the semantics of what I said, but I basically mean that a regular RCA cable will work with the digital signal. I don't think anyone can disagree with that, right?
    I think everyone can disagree with that. Digital coaxial uses a coaxial cable with a single, solid core wire, as the name suggests. The cable is 75 ohm, however most coaxial RCA cables end up having an improper impedance due to the use of heavy RCA connectors, not a problem when it's only a few ohms off, say 72, but it's often beyond allowed tolerance and can cause problems with longer runs. This is why many AV enthusiasts replace the female RCA plugs on their hardware with BNC connectors, and use BNCs on their cables as well. Those are true 75 ohm plugs.

    Analog RCA cables use stranded wire, and the impedance is not especially important for analog use, only the capacitance. But they are not 75 ohm, they are generally around 50 ohm, and they often don't have the necessary bandwidth for digital audio. I personally use coaxial cable for video, digital audio and some home theatre analog audio connections, but never in the car where I need flexible interconnects. I use twisted pair for that. But you should always avoid using non "digital" RCA cables for spdif connections, and of course for video as well, which requires a much higher bandwidth than both.

    You will probably be okay with short 3'-6' runs (3' is the shortest length allowed by the spdif specs), and there is some room for error, but it can affect the sound very noticeably even though it's a digital signal, or not work reliably if at all. RG59 is more than adequate for spdif, and is usually more flexible as well. You don't need to waste money on an expensive digital RCA cable, a coaxial RCA for video use will work just fine. I make my own. The most common problems people experience when using analog RCA cables for spdif connections are the dolby/DTS/THX symbols not lighting up, because the receiver doesn't get all the information due to the inadequate cable. And if you search the various AV forums you will find plenty of people who noticed a substantial difference in sound when they switched to the proper cable.

    I'm using a stranded core coaxial cable made by Belden to output from my M10k, but it's nothing like a stranded analog RCA. There's a lot of debate on stranded vs solid coax. I don't think it's an issue, at least not for car use and short runs. Solid wire is supposed to be the best medium for digital transmission though.


    I'd say it equals my headunit.
    Well, my comments were based on two Creative cards as I mentioned. The $150 Audigy platinum and a terrible, overpriced USB Audigy. They don't come anywhere close to digital and they certainly don't come close to my last HU. I'm sure there are high end cards out there that sound great, but I haven't tried any.

    You mentioned the preamp in Winamp. I would avoid using that. When I increased it's level above 0 you could hear the sound quality suffer so I'm leaving that setting flat.
    I don't use it, although I do use the preamp in ffdshow currently, as a lot of my OGM and MKV videos have low volume compared to music, which can be painful when switching windows in RR. But I'm still experimenting with settings. I can't remember if the sound suffered or not when I played with the Winamp preamp.

    The one fault of this sound card is that the output isn't high enough.
    An active EQ or line drivers would would go a long ways toward eliminating any noise, and allow you to turn your gains down. There are quite a few that boost to 13v.

    At this point I am going to say that an all computer system using an analog out can be comparable to a headunit.
    I definitely agree, but based solely on my limited experience I draw the line at the higher end, unamplified head units I have used in my last few installs.
    In progress: M10000; Travla c134; Xenarc 700TSV; Hitachi 80GB 2.5"; 256MB ULP; M2-ATX; ITPS; Powermate; iKEY SL-88 KB; Holux GM-210; Audiobahn ADD51T w/ COAX/optical converter; Road Runner; iGuidance 2.1

  2. #152
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    very nice post fonesca! I was going to respond, but I don't need to now!

    Jan Bennett
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  3. #153
    FLAC
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    Quote Originally Posted by fonseca
    I think everyone can disagree with that. Digital coaxial uses a coaxial cable with a single, solid core wire, as the name suggests. The cable is 75 ohm, however most coaxial RCA cables end up having an improper impedance due to the use of heavy RCA connectors, not a problem when it's only a few ohms off, say 72, but it's often beyond allowed tolerance and can cause problems with longer runs. This is why many AV enthusiasts replace the female RCA plugs on their hardware with BNC connectors, and use BNCs on their cables as well. Those are true 75 ohm plugs.

    Analog RCA cables use stranded wire, and the impedance is not especially important for analog use, only the capacitance. But they are not 75 ohm, they are generally around 50 ohm, and they often don't have the necessary bandwidth for digital audio. I personally use coaxial cable for video, digital audio and some home theatre analog audio connections, but never in the car where I need flexible interconnects. I use twisted pair for that. But you should always avoid using non "digital" RCA cables for spdif connections, and of course for video as well, which requires a much higher bandwidth than both.

    You will probably be okay with short 3'-6' runs (3' is the shortest length allowed by the spdif specs), and there is some room for error, but it can affect the sound very noticeably even though it's a digital signal, or not work reliably if at all. RG59 is more than adequate for spdif, and is usually more flexible as well. You don't need to waste money on an expensive digital RCA cable, a coaxial RCA for video use will work just fine. I make my own. The most common problems people experience when using analog RCA cables for spdif connections are the dolby/DTS/THX symbols not lighting up, because the receiver doesn't get all the information due to the inadequate cable. And if you search the various AV forums you will find plenty of people who noticed a substantial difference in sound when they switched to the proper cable.

    I'm using a stranded core coaxial cable made by Belden to output from my M10k, but it's nothing like a stranded analog RCA. There's a lot of debate on stranded vs solid coax. I don't think it's an issue, at least not for car use and short runs. Solid wire is supposed to be the best medium for digital transmission though.
    Ooookay. I delete what I said about the cables.

    Did you see where I mentioned about the output levels of the Chaintech card? At first I said they were low, but then I found out the preamp gain on the secondary EPX2 inputs were turned way down low. I think the cards output levels should be fine for almost all amps to run at minimal gain settings. I'll post back once I try it out and see.

  4. #154
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    Quote Originally Posted by JasonWW
    Ooookay. I delete what I said about the cables.

    Did you see where I mentioned about the output levels of the Chaintech card? At first I said they were low, but then I found out the preamp gain on the secondary EPX2 inputs were turned way down low. I think the cards output levels should be fine for almost all amps to run at minimal gain settings. I'll post back once I try it out and see.

    from what i remember, the rf is actually a line driver of sort... it puts out more than it takes in..... there is a level set procedure, look it up in rf archives....

  5. #155
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    Quote Originally Posted by turbocad6
    from what i remember, the rf is actually a line driver of sort... it puts out more than it takes in..... there is a level set procedure, look it up in rf archives....
    No, not really a line driver as those tend to mount by the head unit and up the signal going to the rest of the equipment in the rear.

    The EPX2 is considered a preamp. It takes in low to 4v inputs and can put out up to 10v to the amps. RF did make a balanced line driver called the BLT-1 (?) for the EPX. It mounted right behind the HU and increased the signal level as well as convert it to a balanced signal. The EPX then has a balanced input that converts it back. For those who don't know, balanced lines are the way to go for reducing noise. Of course digital is even better.
    I'm considering using the Julia audio card because it has balanced outputs. I'm waiting to hear back from the guy who made the EPX (Wayne Harris) to find out if the 2 are compatible. RF tech support didn't know much about it.

    There IS a level setting procedure, but it's better to set the gains on the EPX manually. I just forgot they were there. They are buried under the setup folder. I had to look at the manual. Always !!!!

  6. #156
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    yeah, that's why I said "... of sort"... to benifit on an rfi level, you would need to mount the brain in the dash behind the radio........

    incidently.... this is one of the things I love about most newer multimedia units... they split the unit & use a seperate "brain" that gets mounted in the rear near the amps and/or processor.... this means really short rca runs & much less chance of induced noise....

  7. #157
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    Quote Originally Posted by turbocad6
    this is one of the things I love about most newer multimedia units... they split the unit & use a separate "brain" that gets mounted in the rear near the amps and/or processor.... this means really short rca runs & much less chance of induced noise....
    Another reason I love the H700. I plan on having <3ft. runs to the amps.
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  8. #158
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    optical is where its at though.....now adays theres very little reason to not use optical.... if you must run rca's... a rear mounted brain is great....

  9. #159
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    optical solved a lot of my problems!

    but keeping RCA runs short is always a good thing if you can't run optical!
    Jan Bennett
    FS: VW MKIV Bezel for 8" Lilliput - 95% Finished

    Please post on the forums! Chances are, someone else has or will have the same questions as you!

  10. #160
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    Since we have several folks here that are familiar with the Alpine 700, how exactly can you control the volume? Would it only be with the Alpine controller or can it be through the PC?

    I always thought the SPDIF was just the music signal without a signal that tells it the volume of the device outputting it. Red/Jan said that she can control the volume through both. I'm wondering how that is possible.

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