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Thread: bit-perfect s/pdif tuning

  1. #1
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    Feb 2005
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    bit-perfect s/pdif tuning

    i plan on running an ASIO compatible soundcard
    Audiotrak Prodigy 7.1, maybe?
    using spdif optical out to an audiobahn dd51t.

    if im my output from the sound card is optical and bit perfect, can i still tune using the pc (VST), or does the tuning need to happen after the DAC in the dd51t?

    ive been reading for awhile and im still trying to put this all together in my head.

  2. #2
    Variable Bitrate
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    I prefer to tune after the PC when using S/PDIF connections.

    If you think about it, the optical connection you are using has a limited resolution depending on the format you're carrying (for CD, it's equal to that of the source CD it is pulling sound from, each sample having 16 bits used to describe the dB level that sample represents). If, assuming you are outputting bit-perfect sound to an off-board DAC, the CD has a sine wave encoded on it with peaks at -6 dB, it is using x amount of that 16-bit CD resolution to represent the wave. If you attenuate that wave via whatever processing you are using, you then (and someone correct me if I'm wrong) lose resolution, because when you finally pipe it out over the optical connection the wave must now be represented using something less than its original resolution...in effect, you "throw bits away".

    Modern techniques for software processing usually convert each sample to a higher resolution as a first step (as in, each discrete level in the recording is now worth two, or four, or whatever), allowing them room to make software adjustments internally without loss of resolution...but in the end, if you are unable to output the results of that process to a matching higher-resolution DAC for conversion to analog, and instead choose to digitally downsample the results back to their original resolution for optical transport, then you subject yourself to losing signal fidelity by rounding errors and other errata.

    I don't know the degree to which this actually affects what you hear...but I'd just rather do my processing off-board and eliminate the PC middle-man. If you are outputting over analog, then the loss in quality is totally up to the internals of your sound card. An optical connection, for me, is a simple way to carry bit-perfect, or nearly bit-perfect sound to a hardware processing device that was built with such considerations in mind.
    I have too much time and too little aggravation in my life, so I built a carPC. ;)

  3. #3
    Constant Bitrate
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    the only prob with using the add51t is that there is no tuning after the pc. all it has are some preset eqs, bass and treble. Thats it! I finally installed mine last night with the spdif coming from comp to add51t and it sounds lik $h!t. Im a huge SQ guy and is sounds lik hammered damm!t. I am not pleased at all. To muddy and muffled. But i havnt tuned anything from the comp. I dont understand how to do that yet from the soundmax drivers. Hopefully using the add51t will work out bc i dont wanna shell out $700 for the alpine setup. But if i cant get it the way i want it then $$$ will not b an object.

    As far as loosing quality i highly doubt the avg ear will b able to tell a diff even if u tune after the comp. First off 99% of the music listened to today is at the lowest quality. Even CD is low quality. So unless ur running an LP in ur car then i doubt ull b able to tell a diff with the tuning.

    But i do agree with u. I would rather do my tuning after the pc. Thats what im used to and prefer.

  4. #4
    Newbie
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    Feb 2005
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    well the add51t is pretty cheap and its small (thats probably part of the problem right there) and yes i am a SQ guy myself, taking my first step into an optical setup in my car.

    if the add51t doesnt work out, then I dont know what I will use, because the setup im building requires a standalone 5.1 DSP. Dashmountable or not doesnt matter. But im finding there is slim-pickins in the mobile auto market.

  5. #5
    Constant Bitrate
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    Yes there is no alternative unless u wanna spend the money the alpine setup. But i got a new board and soundcard coming tom. Ill post back with my findings tom.

  6. #6
    Car Audio Moderator durwood's Avatar
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    Doing all the VST tuning with the computer and sending it to an audiobahn unit? What is wrong with just using the PC? Are you worried about noise is that why you want optical out?

    I have zero noise coming straight out of the PC from my Audiotrak Card to my amplifiers.

    There are plenty of ways to get surround sound processing in VST form as well if you were worried about 5.1 setups.

    Are you planing on running an active crossover setup or did you want a 5.1 setup? If you want both better look at a card with more outputs.

    Not sure what your goals are, if you define them a little better it might make more sense to do one over the other.

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