I’m back from Chicago. The 2017 edition of the AXPONA is behind me and will most likely be the last time I assemble a real high-resolution, surround music system. We were unique in offering a room that provided high-resolution, surround music. While there were other rooms with multichannel playback — including Dolby Atmos systems — they played movies not music. I’ve read a couple of online reports that gave “Best of Show” nods to other surround rooms by authors that didn’t experience our room. It’s a major challenge for a small company like mine to pull together sufficient support from partner companies to setup a proper surround demo. In fact, if you missed the AIX Records room at this year’s AXPONA show, it’s unlikely that you’ll get another chance. For a variety of reasons, I won’t be back in the new convention center venue with a full demo room. I may show up with a sales table to offer my book and software, but the days of a full 5.1 system are behind me — at least at AXPONA.
I read an article on DAR that addresses the pressing and persistent question about variations in “quality” when using USB digital connections. I’ve always maintained that digital connections do not, should not, and in fact, can not affect the “fidelity” of a reproduced audio file. And despite the title of the article on the DAR website (“Gordon Rankin on why USB audio quality varies“, I stand by my assertion. I not going to dwell heavily on the content in the piece as I acknowledge that Gordon Rankin, the founder and chief engineer at Wavelength Audio, knows more about the USB format than I do. You should visit the DAR site and read the piece for yourself.
The bottom line is that USB needs small (and expensive) devices to help it do its job (Regen, Schitt Wyrd, Jitterbug, iPurifier etc). Gordon is quoted in the article as saying, “For USB audio, the receiving device is basically translating a serial stream of data with a clock interwoven throughout. At the end of the packet sits some sort of block check. If the block check does not match the data then that packet is flagged as an error.”
“With Isosynchronous USB transmission, packets are sent without any error correction / resending. But guess what? This is the USB protocol used for audio frames. The bad news is they are not error free. The good news is these Isosynchronous frames are afforded the highest priority in the system.”
He goes on to discuss a series of tests that he’s done that conclusively show CRC errors occurring in USB data streaming. I agree wholeheartedly. Error can and do happen rarely during the transmission of data from a source to a remote DAC using the Isosynchronous USB transmission protocol. However, the critical question is what happens to the sound that is converted from a stream with CRC errors in it?
As a mastering engineer for many years, I could see the CRC error light on my Sony 1630 processor (a mastering machine used to convert analog to digital and digital to analog when preparing a CD using a U Matic 3/4 inch video deck) go on and off on occasion. But the analog output didn’t glitch or drop out unless there were a lot of CRC errors. But most importantly, a CRC error as reported by Mr. Rankin doesn’t ever impact the fidelity of the output. If purveyors of boxes like the Regen tell you that the fidelity of the resultant sound is somehow enhanced, they’re marketing not informing. A CRC error would produce a sudden drop out or “snat” not a color or timbre change. I’ve heard plenty of drop outs in my 20 years of engineering using digital equipment. Gordon’s right when he says that USB can have “quality” issues. What is not made clear in the piece is that the quality is an all or nothing affair when the analog playback is experienced. You either hear the music or you don’t. How many times have you experienced a drop out when using your external DAC? I would guess not very often.
I can confidently state that you’ve never heard a timbral or fidelity change when connecting a digital source and a destination using a USB cable. Of course, you need a good USB cable ($10 will do) and a high-end DAC that doesn’t depend on the clock accompanying the digital data in the USB cable. As I’ve said before, any self respecting DAC manufacturer will “reclock” their devices so the quality of the clock is independent of the cable and source clock.
So digital transmission errors are never a good thing. But it’s important to know what sonic effect errors can produce. In the case of CRC errors, they aren’t really a problem in current high-end audio playback systems.