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Need both Coax and Optical inputs on an external interface

Discussion in 'Recording' started by pfm, Feb 22, 2012.

  1. pfm

    pfm Active Member

    Hi!
    I am looking for an external (usb preferred but firewire not ruled out) interface or "sound card" that has both digital coax as well as optical spdif inputs.
    So far I haven’t been able to find one that has both. It’s mostly optical and some have coax only, but never both (or atleast I haven’t found one yet). Any pointers or directions would be highly appreciated!
    Price range - I'd say if I can manage to get something under $200 that'd be great, but I can look for a used one too (if I can figure out what to search for!)
    Thanks!
     
  2. RemyRAD

    RemyRAD Well-Known Member

    There is nothing wrong in wishing to go to the moon for $200 though, perhaps a little impractical at that price. I have a unit that does both of what you want. Unfortunately, it requires a desktop computer with a PCI slot. And the device was over $700 10 years ago. So with the computer, it was a couple grand. The unit is/was the MOTU 2408 MK-II. And it has 8 analog inputs/outputs along with 24 tracks of TA-SCAM TDIF & 24 tracks of ALESIS ADAT, Optical and coaxial SPDIF. Though there is probably something out there that comes close for you but probably not in that $200 range. Why do you need both? You're not listing any other equipment? Are you sure your car doesn't need Regular and Premium together? Do you play both acoustic and electric guitar, simultaneously? Drums and keyboard at the same time? No I didn't think so. Maybe instead of asking us about a non sequitur use of a piece of equipment it would be better if you just tell us what you're trying to do? While I use all of my digital and analog inputs and outputs, I don't use them at the same time simultaneously. Though they do get utilized sequentially. But these are only in specialized applications and if I told you what and how I was using all this stuff... I'd have to kill you.

    It's your move and you're it.
    Mx. Remy Ann David
     
  3. Boswell

    Boswell Moderator Distinguished Member

    Can you tell us why you need both inputs?

    If it's to record two stereo digital inputs at once, you have the problem of synchronizing the sources so that they can be correctly recorded, as the sound card can only lock to one source or the other.

    If it's because you have devices that have different sorts of S/PDIF digital outputs but you do not need to record more than one at a time, then the easy solution is a coax-optical or optical-coax converter. These are the size of a matchbox (plus a wall-wart power unit). You buy the direction you need and they cost only a few $. I have a couple of each direction for the odd times I need to connect up random S/PDIF units. If you have one of those you can choose a standard sound card that has either the optical or coaxial S/PDIF input and then you can use either type of source device. A number of computer motherboards these days have coax S/PDIF inputs, so you may not even need an external sound card or audio interface.
     
  4. pfm

    pfm Active Member

    RemyRAD, Thanks for the warm welcome!

    No, I am not going to use both inputs simultaneously! One at a time only. I wasn’t sure how much boring detail to put into my first post so here goes –

    I am not a recording engineer in a studio but I am a diy audio enthusiast. I build and/or improvise speakers, amps, dacs – for fun - or perhaps just chasing the desire for a real and good sound of music. Yeah I have a turntable (Thorens TD-165) and a R2R recording machine too (Pioneer RT-707). So while not exactly what you do about music and recording per se, its still more or less the same thing. Especially the hardware, and that’s why I came to this forum for this question as you guys might have a wider view of product options than on a typical consumer audio forum.

    The choice for multiple inputs was driven by the need to interface with devices that may or may not have one or the other input. Part of this is also about doing a test to determine which of these two interface transmits the original content from the source faithfully, and if it does not then why.

    But yes getting a good converter is certainly an option. Don’t know why I didn’t think about that. Thanks for the suggestion. Although the soundcard would have to be coax because if its optical and then I convert to coax it defeats the purpose of what I trying to do because optical is already converted from 'coax' so to speak (electric to light). Any recommendations or pretty much any brand name converter should be good enough ?
     
  5. Boswell

    Boswell Moderator Distinguished Member

    The S/PDIF data stream has identical content in electrical (RCA Coax) or optical form. You can convert from one to the other as many times as you like. Although each conversion may introduce a small delay and an additional risk of corruption, the data content of a correctly-converted bitstream does not change.

    Almost any make of converter should work as long as you keep the coax and optical cables reasonably short.
     
  6. RemyRAD

    RemyRAD Well-Known Member

    You are basically confusing numeric digital transfers in the same realm as the degradation that comes from dubbing from one tape recorder to another. That doesn't happen in the land of digital. You're only transferring ones and zeros in precise mathematical methods. And having digital inputs and outputs is a completely faithful way to transfer from one piece of equipment or medium to another, flawlessly, in a lossless way. Going from analog to digital and digital to analog can introduce level differences and distortions. Along with their latency of delay. Sometimes one needs to compensate for these delays in their software, manually. Other software will make the corrections for you automatically. And software is as personal to one's self as their choice of underwear is. Are you wearing the correct underwear? Don't answer that. We don't want your girlfriend to find out you are wearing her panties. Obviously with that scenario, you feel completely different under your bluejeans. And how would one to know?

    Simple USB soundcard devices generally don't have much in the way of digital input/output ports. More expensive devices frequently offer numerous different analog and digital ports. Cadillacs have more creature comforts inside than Chevrolet Impala's for instance. Yet there drivetrain may be nearly identical. So the only real difference is your comfort level. Digital ports always yield digital clones when things are transferred. There is no additional mathematical crunching in that equation or execution thereof. There is however when one goes from analog to digital, digital to analog and back again numerous times. Then you experience degradation from the amount of translations through the analog electronic portion of your converters. Better converters have better analog stages within than cheaper converters have. And therein lies the greatest difference in cost. Quality analog stages within a converter can be quite costly in comparison to a simple and inexpensive IC chip as utilized in most general consumer oriented devices which of course are hugely more affordable. There are scenarios however where if one makes too tight a turn with an optical fiber cable, data can be skewed which can cause horrendous sounding digital atrocities to occur. Even electrical Copper COAX Cable can screw with the digital bitstream if doubled over itself and/or even being walked on, could and does occur.

    Flatlining can be both good or deadly
    Mx. Remy Ann David
     

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