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Thread: audio over USB v. optical

  1. #1
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    audio over USB v. optical

    Let's just say that you have an outboard unit (like a DAC) that will convert the audio stream from digital to analogue.

    What do you see as the pros and cons to USB over optical?
    __________________________________________________ ___________________________________________
    EDIT: Since this thread has taken on it's own identity, I'm going to post this up here at the top to help explain what's going on here and what my intent is with this idea.
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    This product, this idea, is all designed as a high end solution that does not currently exist for the relatively small population out there that is interested in high end audio. It was never intended as a vast consumer solution, as there are already plenty of those avaliable.

    Everyone needs to remember, when starting out designing a product, you cannot implement the features that everyone wants, and you cannot implement the one off features that one or two people want. This product needs to be useable to the most people possible (the most high end users at this point). As such, the list below has been set forth at this point in time.

    We now have a list of desired features:
    • USB connection to the PC (this is because USB is most readily avaliable, Firewire will be next once this is underway)
    • 5 pair of RCA outputs (again, this will be adjusted once we know things work)
      • at least 4V outputs, prefered to have 8V
      • socketed RCA sockets - so that the end user can opt to upgrade the sockets if desired
    • User replaceable OpAmps
      • User replaceable caps would be nice, but not necessary.
    • 12v DC power supply, able to be run on unregulated 12v DC would be even better.
    • Encased in an external enclosure - much like a DAC or an external sound card
    • Size is of concern, we need it to be small enough that it's easily able to be hidden. Nothing like the size of the DBX drive rack and the like. Something along the same size as the Alpine 701 brain.


    with this we can now start to look at building a prototype. I've contacted Douglas and asked him to take a look at this thread and if he wanted to register to give us some input. We'll see. Else I've got a few other contacts I can go after.
    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!

  2. #2
    cheap custom title JC-S60's Avatar
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    The biggest pro for an USB DAC over spdif is the fact that it is two-way communication with acknowledgement of received packets by the receiving end - and a re-send of the packet if it got lost along the way (no ack).

    Simply put: there is no jitter caused by the transport of audio over USB, while spdif can have some jitter.

    Joachim

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    Car Audio Moderator durwood's Avatar
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    I thought there still was jitter across usb since it relies on clock cycle. And even though USB is bi-directional I thought that audio over usb is still only one way? Am I wrong? Is there error checking in there somewhere?

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    MySQL Error scott_fx's Avatar
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    i thought so too
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  5. #5
    Car Audio Moderator durwood's Avatar
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    Something I found although I know there is a lot more info out there. I remember reading a lot of it but just disregarded because I wanted the computer to do audio processing which ruled out USB DACs.

    http://forum.stereophile.com/forum/s...7819&Main=7334

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    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    I've seen arguments each way.... the only way I've seen to really eliminate jitter is to use an inboard pci or a solution that uses a word clock & a pci board to sync it, but... how much jitter? truth is, it'll probably be an inaudible amount, & if you don't hear it, is it really there?

    this may be a good place to ask again, does anyone know if multiple usb dac's can be used, & there any reason this would be a bad idea?

  7. #7
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    I'm not sure on the multiple USB dacs.

    I'm asking because I'm tossing around the idea of looking into having an outboard DAC built that would have multiple RCA level outputs with high voltages. Something that has replaceable opamps and possibly other components.

    I'm wondering if it would be better to go over USB or over optical.

    Seems to me that USB would be the best bet since not all computers have optical outputs.

    What options would you think would be desireable for something like this?

    I'm thinking about 10 outputs (5 pairs).

    Heck, maybe even making the board it's self but making it a project type board. That way, if I wanted to use the WBT sockets, but someone else didn't want to spend that much money, it's all an option. Same with the DACs and with the other components.

    Something where you can pick the RCA sockets you want to use. The caps, the opamps, etc.

    But since I know literally nothing about doing somehting on this level, it's going to take some collaboration.

    This would be something that's an audiophile upgrade for most folks with CarPCs. Once something like this is done, we could approach a developer about integrating all of the software into one program...or something that could be integrated into a front end.
    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!

  8. #8
    Car Audio Moderator durwood's Avatar
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    I see. Can I bring up another point? What about Firewire? I know it's not as common as USB, but firewire has more bandwidth. Or do we even need to worry about bandwidth? Does Firewire suffer from Jitter? Why aren't there more Firewire Dac's? So many questions...

  9. #9
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    I think the initial version would need to be something that's capable of being used on the most PCs. If it works, then we can look at a FireWire version.

    BTW - even though I'm working for StreetDeck/MP3Car.com right now, this isn't something I'm researching as part of the company. It's something I'd personally like to see designed and built. If it takes off then possibly we can have it manufactured. But I think this might be something that's done simply on a hobbiest basis currently.
    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. #10
    Car Audio Moderator durwood's Avatar
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    Ok I pose another question for you:

    What do you want handling the processing? Were you thinking let the CPU handle it (currently what we have available with the VST effects) or do you want the DAC to handle it all?

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