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Thread: audio over USB v. optical

  1. #11
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    As turbocad said the best way to eliminate jitter is probably running a Wordclock.

    This may be entirely not an option, but have you considered running ADAT. You'll have the wordclock to eliminate jitter and can run 8 channels easily.

  2. #12
    Constant Bitrate Felix509's Avatar
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    Talking Some Answers

    Long time lurker, and my first post here... I have done research on this for my home system and have some documents saved on my compter, not sure where they came from exactly, i think from the USB DAC product description pages...

    QUOTE::

    Basically the DAC has a single digital USB input. USB unlike SPDIF is bidirectional and therefore has error correction and buffering on both sides. This happens automatically so the data on the disk is identical to what is going out all the time. Also since this interface is asynchronous the clocking problems associated with SPDIF go away. What happens is... On power up of the computer the 2 devices negotiate services. In this case the USB DAC tells the computer it can do 16 bit audio at 32K, 44.1K and 48K. Since the USB receiver only has to handle these 3 frequencies, the clocking to the separate DAC IC has almost no jitter. SPDIF actually has to be synched to the exact frequency of the transport (i.e. if the transport is working at say 44.0896K instead of 44.1K the dac has to sync to that frequency). Therefore the jitter problems of SPDIF almost go away using USB. So using USB we have a zero error protocol to link the computer to the DAC and very low jitter what else.....

  3. #13
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    Quote Originally Posted by RedGTiVR6 View Post
    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.
    hey red,

    you may want to contact Douglas; the guy who built the hpdac that i have. He designed and built that dac/amp with good results. maybe he could steer you the right way
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  4. #14
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    Quote Originally Posted by Felix509 View Post
    Long time lurker, and my first post here... I have done research on this for my home system and have some documents saved on my compter, not sure where they came from exactly, i think from the USB DAC product description pages...

    QUOTE::

    Basically the DAC has a single digital USB input. USB unlike SPDIF is bidirectional and therefore has error correction and buffering on both sides. This happens automatically so the data on the disk is identical to what is going out all the time. Also since this interface is asynchronous the clocking problems associated with SPDIF go away. What happens is... On power up of the computer the 2 devices negotiate services. In this case the USB DAC tells the computer it can do 16 bit audio at 32K, 44.1K and 48K. Since the USB receiver only has to handle these 3 frequencies, the clocking to the separate DAC IC has almost no jitter. SPDIF actually has to be synched to the exact frequency of the transport (i.e. if the transport is working at say 44.0896K instead of 44.1K the dac has to sync to that frequency). Therefore the jitter problems of SPDIF almost go away using USB. So using USB we have a zero error protocol to link the computer to the DAC and very low jitter what else.....
    that quote looks like it may be from the wavelength site.... they seemed to say the same thing I think...


    I have searched all over, & just about all of the really high end outboard dac's are just 2 channels....

    I have found some really awsome external usb dac's, but nothing with a lot of channels...

    I also considered using optical out into a real rack mount dac that has muliple channels, like an apogee... the concern there is, the rack mount will be designed for 110 & the power supply is critical... it would need to be re engineered in the power supply area for sure, but this may be an option? kinda like the ranes used to be done for eq....

    at this point I think that all eq & xovers should be on the pc, but I did consider also going passive for the xovers which would lighten the load significantly on the processor, but then phase shift won't be able to be addressed & time alignment, which is critical at least for the sub to me, plus passive is wasteful power wise.....

    theres also an outboard firewire dac that has multiple channels & also does some processing... it's called a power core system by tc... looks like it runs plugins on it's own processor & it has ram on board, but I'm not sure if the software for that would meet our needs, it's more designed for recording, which it seems most of the high end stuff is more geared towards... studios don't do what we do with multiple channels for one set of speakers on the output side.... they do mention it running vst plugins, but I'm not sure if that means theres or any...

    they do make a smaller more portable power core too, might be the traveler? or I may be just thinking of the motu..., just looked it's called power core compact

  5. #15
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    Quote Originally Posted by Felix509 View Post
    Long time lurker, and my first post here... I have done research on this for my home system and have some documents saved on my compter, not sure where they came from exactly, i think from the USB DAC product description pages...

    QUOTE::

    Basically the DAC has a single digital USB input. USB unlike SPDIF is bidirectional and therefore has error correction and buffering on both sides. This happens automatically so the data on the disk is identical to what is going out all the time. Also since this interface is asynchronous the clocking problems associated with SPDIF go away. What happens is... On power up of the computer the 2 devices negotiate services. In this case the USB DAC tells the computer it can do 16 bit audio at 32K, 44.1K and 48K. Since the USB receiver only has to handle these 3 frequencies, the clocking to the separate DAC IC has almost no jitter. SPDIF actually has to be synched to the exact frequency of the transport (i.e. if the transport is working at say 44.0896K instead of 44.1K the dac has to sync to that frequency). Therefore the jitter problems of SPDIF almost go away using USB. So using USB we have a zero error protocol to link the computer to the DAC and very low jitter what else.....
    welcome felix. thanks for the useful post
    New System in progress:
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    Phaze TD1500 ~> Dynaudio MD130
    Phaze TD1500 ~> Seas g18rnx/p
    Zapco Ref 500.1 ~ 12" tc-9
    Behringer DCX2496 ~ Envision Electronics psu
    Transflective Xenarc

    My Car Pc Install
    My Boat Pc worklog

  6. #16
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    I think audio over USB is only going to get better. Windows Vista promises to do a much better better job of insuring quality with the new new Intel HD Audio Architecture, I think it's the way to go.

  7. #17
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    my front pc uses an intel 915 chipset that includes intels hd audio onboard... this works on xp though, I thought that was more hardware than software... will it do anything different on vista other than allow multiple volume levels for each ind. app?...

  8. #18
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    Quote Originally Posted by turbocad6 View Post
    my front pc uses an intel 915 chipset that includes intels hd audio onboard... this works on xp though, I thought that was more hardware than software... will it do anything different on vista other than allow multiple volume levels for each ind. app?...
    Not really sure, I know there is strict testing to ensure products that bear the new "Designed for Windows" logo meet the UAA design requirements which means that the audio over USB will work correctly unlike some prior sloppy USB over audio implementations.

  9. #19
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    that's worth looking into... I did a bit of looking into intels hd audio, but not how it may be affected by vista.... or how usb audio could be affected..., I know they did some work with audio in general.... hmm...

  10. #20
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    Quote Originally Posted by durwood View Post
    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?
    I pose that the PC still do all of the processing.

    My thinking is that if this works out, it can be an option for those of us who are serious about SQ.

    I'm willing to do a good deal of leg work on it, but I want to do my research first.

    I'm pretty sure we have 4 takers in this thread alone if it can be done. Though, who knows how long it will take....lol

    Basically, I'm thinking it would be like a sound card and a DAC all rolled into one....if that makes any sense.

    Only it caters to the CarPC market.

    At first, it will be more of a personal project more than anything else. If it's successful, then I'll see about our other options.
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