I've been really unimpressed by the level of speculative and anecdotal 'evidence' permeating the USB cable related threads. The levels of selective reading and blind faith spiced by unnecessary spending and delicious placebo are to say the least astounding and as always do little/no favours to credibility of audio community and vendors. So I've decided to email http://www.usb.org/about - a non for profit forum founded by the developers of the usb specs, to find out some more authoritative answers to the questions of both USB cables and (as it turned out, I didn't ask, but the responder addressed) bulk vs async vs adaptive USB transfer modes. "If anyone would know - it's them" is my way of looking at it. To my surprise they've replied to my initial email, and will hopefully reply to follow up questions. You're welcome to ask any additional questions and I'll pass them along (probably more convenient for the people on the other end if it all comes from a single contact) Of course the more selectively reading gifted of us will read in more magic and speculation, but I hope this will clear up some issues to people who really do want to know the hopefully objective facts behind it all, from people who don't have a financial interest in selling audio cables, gear or advertising in magazines. Or perhaps, while we're waiting for some objective measurements from people without vested interest/the right set of equipment and skills to conduct them. Anyway, here are the org messages so far (waiting for a reply to the follow up atm) (my name and email removed, the email of the usb.org people separated by AT to prevent delicious spambots harversting) -----Original Message----- To my surprise the reply also unexpectedly addressed the issue about adaptive/async transfer modes vs bulk mode usb audio devices. I've long thought bulk mode was superior because of error detection and retransmission and it seems usb.org people are of the same opinion. You can view the org deliberations about it in http://www.head-fi.org/forum/thread/546092/confirming-whether-your-dac-is-asynchronous-as-claimed-or-not I obviously don't advocate musiland products, in fact I'm vocally opposed to their dodgy QC, and bs marketing, that's probably quite clear from say, 3 threads from me catching them on their bs . Bolds are on my side for emphasis . -----reply 1----- [quote name="TechAdmin [AT] usb.org"] to svyr date Fri, Aug 5, 2011 at 5:46 AM subject RE: usb audio (class 1 and 2) and cable affecting sound? Hello [svyr], USB transmits information digitally. Bits are either received correctly or not received. What a bit looks like on the wire has no effect on quality if the bit is received correctly. If a bit is not receive correctly, error checking in USB protocols will flag the error in data transmission. Jitter is not a cable problem. Jitter is a transceiver (PHY) issue on the devices. Can bits get scrambled within a cable assembly on occasion? Yes, primarily due to EMI but this is highly unlikely -- more on that later. Is occasional data scrambling a problem for audio/video? Maybe. The answer depends on the hardware receiving/rendering the data. USB supports isochronous transport which is a timely delivery of data. The isochronous transport has guaranteed bandwidth on USB. Isochronous protocol, however, does not support error recovery. In other words, if data is flagged as an error by the receiver, there will be no attempt at data retransmission. So if the receiver is using the isochronous protocol, then there can be errors in data. Most webcams use the isochronous transport. High-end audio/video equipment that does not mandate real-time delivery of data should not use the isochronous transport because accurate data delivery is not guaranteed. USB also supports bulk transport. The Bulk transport shares bandwidth and timely delivery is not guaranteed. Bulk protocol does have error recovery and errors in data will be retried. If the receiver uses the bulk USB protocol, then there will be no errors in the data. This is why USB mass storage devices always use the Bulk transport. Most USB audio/video devices use the bulk transport because real-time delivery of the data is not necessary. Bulk audio/video devices will buffer data before rendering it. I can think of only two situations where the audio/video will be disturbed when rendered: 1) If the host is busy performing IO to other USB devices, or 2) There are errors in data transmission where continual retries cause buffer under-run to occur. The second point could be cable related -- it could also be poor hardware design of the host or peripheral as well. The USB Bulk transport works very nicely for audio and video because data is accurately delivered. Now onto cable quality. A cheap USB cable will work perfectly fine in the vast majority of home/office environments. All USB certified cables use certified connectors and are shielded, have minimal skew on the data lines, and meet criteria regarding impedance and voltage drop. If the environment is extremely noisy with EMI, then a better shielded cable may be necessary. Usually relocating the cable or power strips will suffice to mitigate EMI. Personally, I would never recommend anyone buy an expensive USB cable unless they are experiencing problems not related to their hardware and there exists definitive suspicions of environmental interference. I do always recommend that the cable purchased be USB certified which provides assurance that the product is properly designed for USB. Using USB certified audio/video equipment also assures that the USB signal quality and other packet parameters of the transceiver meets specifications. Of course, all of the above is premised upon properly designed and functioning hardware. Regards, Mark Paxson USB-IF Compliance Administrator TechAdmin@usb.org (ReplyID 110804.105337) Please visit http://compliance.usb.org for the latest updates to the USB-IF Compliance Program. [/quote] again, I trust that's about as clear as it could be about cable jitter, and transfer modes. More info about usb transfer modes and adaptive vs bulk vs async and the associated lack or presence of error detection and correction is in. http://www.head-fi.org/forum/thread/546092/confirming-whether-your-dac-is-asynchronous-as-claimed-or-not I obviously don't advocate Musiland, in fact I'm vocally opposed to their dodgy QC, and bs marketing, that's probably quite clear from say, 3 threads from me catching them on their bs Anyway, I thought I'd ask a few more questions: -----follow up message----- So I'm currently waiting for a reply to those... I hope this sheds some objective light on the usb cable issue, and will make more USB audio makers get off their lazy backsides and make DACs with proper bulk transfer mode USB implementations (I can't be angry enough with musiland being the only one from the audiophile market to date that do it)...Writing drivers is difficult, especially for multiple OSes, but is it a good enough reason to continue making adaptive/async usb transfer mode DACs instead of bulk mode ones.