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On USB cables and controller transfer modes (a series of questions to/replies from usb.org)

Discussion in 'Computer Audio' started by svyr, Aug 5, 2011.
  1. Roller


    Well, despite USB Audio continuing to remain similar to what it's been so far, there are definitely issues with all sorts of audio devices plugged to USB 3.0 ports, tested on a multitude of systems (both computer and DAC wise) which is something that doesn't happen with USB 2.0. I'm very much curious to know what might be the reason behind this, and the whole rough road that USB 3.0 adoption has certainly didn't do any good to avoid things like this.
  2. skeptic
    Great post svyr!  This deserves a sticky.
  3. svyr

    you might want to specify the DACs (and the USB receiver chip) and the USB 3 controller chips for a more concrete answer
  4. Roller


    I understand what you mean, but I'm actually saying that every single report when it comes to USB3 and DACs (haven't heard of that new Musiland DAC, though) show that there are audio dropouts, crackling, hardware recognition failure, high DPC values, etc, on both newly installed machines and long running ones as well. I should add that all those reports are at least 3 months old, though I'm not aware of any new USB3 controller chip being released to market that could've solved those issues. Basically, I haven't heard of any positive feedback anywhere about using (USB2) DACs with USB3 ports.
  5. 00940
    I wonder if the guys at USB.org have actual data on the distribution of protocols (bulk, adaptive, asynchronous) in function of the sales, for USB audio devices.
    Up to now, the majority of devices I've seen advertised on head-fi use isochronous adaptive USB receivers (and a significant minority asynchronous ones), as they do not require special drivers and are the simplest to implement. I think I can count on the fingers of one hand the devices using bulk mode.
    Their statement that "Most USB audio/video devices use the bulk transport because real-time delivery of the data is not necessary" might be true, but certainly not for the sample of products bought by head-fi users.
    svyr likes this.
  6. svyr
    >Their statement that "Most USB audio/video devices use the bulk transport because real-time delivery of the data is not necessary" might be true, but certainly not for the sample of products bought by head-fi users.

    that's what I told the guy as well. IDK, maybe he meant USB headsets or something :D ...

    I've just sent him a follow up email on the two questions now. Although he probably realized if he continues replying, he'll probably be spending a bit of time and there will be more questions

    I think EMU series USB cards might use bulk mode as well, but not too sure (might be async as well). Maybe 2-3 more in the pro audio or audio-unicorn world :D ...

    a large majority of head-fi DACs or transports with USB section definitely use isochronous adaptive mode. Maybe 5% use asynchronous if not less.
    And as I said in the post above I also very strongly suspect the proliferation of adaptive mode DACs seems to be simply because it requires the least amount of effort (slap it in, no additional firmware or drivers, and simply output to I2S or something...)

    It's pretty doubtful that USB.org would have any sort of stats, since it's more to do with the number of chips supporting adaptive and async modes and the willingness of manufacturers to use bulk mode... or rather unwillingness. (and who can blame them if you need a driver for win, lin/mac (and potentially firmware on the receiver side in case you don't get it right on the first go)....Although a reference implementation could've been provided by USB.org or whoever else to assist, but you know... every receiver would have its own quirks/every major OS upgrade might also have audio related OS changes...Development and maintenance of the firmware and driver code is not an easy or cheap task, and why bother if people buy adaptive anyway and then just say 'oh no adaptive is just as good, it's all down to implementation' (that's marketing BS, for adaptive it seems to be about the USB receiver chip itself and its stability, jitter, etc...since you're just vanilla connecting that to the I2S on the DAC, or ASRC, or reclocking of some other sort, but hey, who are we to kill unicorns))
  7. DaBomb77766
    It's kind of funny how there's almost no discussion going on here in this thread, but the debate goes on in other threads.
  8. blacknile
    Thanks for the effort, really appreciated. I believe you should post this reply on other forums as well - I'm thinking of computer audiophile for instance, where claims about the superiority of UBS cables costing 10 times as much as standard ones are made daily.
  9. Roller
    For the time being, there doesn't seem to be any progress on the whole USB 3.0 issues, which means I'll have to get USB 2.0 cards in the future in order to get issue free USB DAC usage, or even completely drop USB on my systems for audio purposes.
    Hopefully, svyr will pop by with any news regarding this situation.
  10. svyr

    I suggest we all spam usb.org with the questions above lol. I haven't received a reply to any of the subsequent questions asked.
    It could be because the admin closed the original ticket after the reply, or is busy, or wasn't amused with the public posting of the emails, or something. In any case more people contacting them with pressing questions from above (just copy paste them :D) or any additional ones could help. (admin AT usb.org)
  11. skrivefeil
    As a side note on the USB 3 matter, my (USB powered) Nuforce uDac 2 prefers my USB 3-port when powering my 600 Ohm Beyers.
    The uDac is officially recommended for 32 - 300 Ohm headphones, but you know, recommended, recoschmended.
    The USB 3 is capable of delivering higher voltage, which in the end means higher current or effect (or whatever you like) to the headphones.
    I figured this out when the amp started making static noise with the Beyers, but not the 38 Ohm ATH-M50s.
    I switched back and forth, always having the same static with the Beyers after a minute or two. None with the ATs,
    Switched to USB 3 = no problem. The uDac 2 is still a USB 2 peripheral, though. It's just that it prefers not to have a 5V upper voltage limit.
    A higher quality USB 2-port, or a powered hub, would probably be just as good a solution, but I haven't had the time to experiment too much just yet.
  12. svyr
    > A higher quality USB 2-port, or a powered hub, would probably be just as good a solution

    depends on the current drawn, a to spec USB 3 hub or port can supply 400ma more than USB 2 (900ma@5v vs 500ma)

    keep in mind, you can exceed the max ic (say, opamp in particular) voltages and or max temp limit, bricking either the ic or the amp.
  13. skipspence
    Might ask them about the USB isolators a-la


    as well. (although that might be more of a question for Analog Devices, who produce the ADUM5000 ADUM4160 chips.
    Edited by svyr - 8/7/11 at 8:19pm
    .... so what about olimex isolators when used with musiland devices? i only ask  because they not fully usb 2.0 compatible ( only 12 Mbps not hi-speed ) - have you tried them and if they work at all?
  14. svyr
    i suspect unless you get a usb 2 high speed (480mbps (well, not that much really, but definitely not 12 as all of the above state they support max)) compliant isolator it won't work properly.

    '• USB 2.0 compatible - Low & Full speed data rate: 1.5 and 12 Mbps'
    I can't say i got 12mbps but I at least got 6mpbs by testing with a USB mass storage device (flash drive). Even in Full speed 12mbps mode the aimagin one stutters

    (despite the bandwidth theoretically being enough for say 44.1k 16b (16*44100 = 705600 bps, or abiyt 700kbps << 12000kbps) - even if you include the whackiest protocol that wastes 12x the bandwidth.

    But, seriously, it must be something else, not just the bandwidth (well, even though according to the above, the bandwidth is more than enough). maybe the way the adum chip works on the data channel - i don't know. I wouldn't buy another isolator based on the same chip for bulk mode devices from musiland.(the cypress usb controller might also be incompatible with these for some reason)
  15. skipspence
    ... yes it's obviously too slow for usb2 speeds ... but i read at least one statement that some devices:  http://www.circuitsathome.com/products-page/usb-interfaces
    had been successfully tested even at 96kHz,  though issues have been reported with some DACs at rates over 48kHz are almost certainly caused by the drivers, and drivers on musiland are bulk mode... anyway i got olimex isolator lately but not tried it yet so will return with some comments after testing. 

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