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DAC USB Audio 2.0 compatability

Posted by 91derlust (A) on December 2, 2016 at 19:48:11

Hi all - thanks for taking the time to read this.

My attitude towards USB 2.0 compliance has been turned upside down. Well, my understanding of where potential incompatibility issues reside has.

In fairly recent history, based on DAC manufacturers demanding USB Audio 2.0 compliance from audio source (server/ renderer/ et al) vendors and what I perceived as a cavalier approach by some of the source vendors to squeeze the last bit of performance from an adapted protocol, I assumed that incompatibility was most likely to reside server-side or perhaps with the USB cable. My experience has backed this up. Until now.

In the past, a Linux-based server connected by USB to my DAC produced frequent, but irregular blips of varying duration and amplitude. Dropped samples? Windows and Mac exhibited no such behaviour. The DAC manufacturer suggested the cause was server-side: its hardware did not reflect the USB 2.0 standard and I had concerns about the compliance of their USB Audio 2.0 code. The server manufacturer claimed their implementation was compliant... The server went back to the retailer.

Another Linux-based server was much better, but on occasion I sensed similar issues, but more subtly; it could have been expectation effect on my part. I persisted and continued to use this server for a year or more, although it is not an ideal sonic match for my system.

Enter my new Linux-based server. You know what's coming: the issue recurred, big time. The manufacturer of my new server is adamant that it's hardware and software are unquestionably USB Audio 2.0 compliant. They make a convincing argument and by all accounts are of high integrity. I will know more after the manufacturer remotely accesses my set-up in a couple of days (they have also been very responsive to questions etc - impressive!).

But all this has me wondering: despite the demands and claims, really, how compliant are DAC manufacturers with USB Audio 2.0? Apparently XMOS was one of the earliest manufactures to provide compliant USB Audio 2.0 firmware with their hardware. What happened before XMOS hit the scene - from where did DAC manufacturers source their firmware? Was the firmware USB Audio 2.0 compliant and how can they prove it? Why the need for frequent firmware updates if compliant? Even with compliant firmware available, are manufacturers hacking their USB firmware, that potentially is non-compliant - again, how would they prove compliance... how thoroughly do they test... across what platforms? Wouldn't a compliant DAC work with compliant servers irrespective of whether Mac, Windows, Linux, or...?

I'll be following-up with my DAC manufacturer, who states its USB input is Linux USB Audio 2.0 compliant. Still, I am wondering what others think?

Cheers,
91.

"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

Edits: 12/02/16 12/02/16 12/03/16

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