John Atkinson, in September's Stereophile Magazine, waxes poetic of Audioquest's new $49 Jitterbug USB 'thingie'. And others I know, including my friend Arnie Nudell, use similar devices that have come to be known as USB regenerators and isolators, of which there are a growing number. I haven't yet tried the Jitterbug in my system, nor the others, though I did hear a demo of the jittered bug at a tradeshow that impressed me, but left my socks on.
I wrote yesterday of hearing miracles on the system and promised today to reveal at least what I was listening to with hints of how you too can get closer to what I heard. Our engineering department has been experimenting with these USB isolation devices and I was asked to try out a very different and specialized approach to the problem of USB cable length. To explain the function of this new device, I'll first need to give you a bit of background. USB is a two-way communication protocol. Simply put, musical data sent from the computer to the DAC is first broken into packets - similar in concept to how DSD is sent over PCM (DoP). Each chunk of music data is preceded and followed by identity and veracity bits that must reach back to the source to give the OK to send the next chunk. If the cable is of poor enough quality, or too long, or both, the return packets fail to get home and the connection is lost. This limits USB cable length to less than about twelve feet.
The prototype PS Engineering asked me to audition removes this limitation, allowing cable lengths of hundreds of meters and, in one setup, miles. Clearly, what I used was not entirely similar to the Jitterbug and other isolators and signal regenerators, though close enough I bring the entire group into the discussion. What are the isolation and regeneration devices I first mentioned? Our Ted Smith explains:
The Regen is trying to generate a USB signal that's clean enough that the DAC's USB PHY (the PHYsical layer, the part that drives and receives the signals over the wire) doesn't have to "work as hard" and hence doesn't add as much noise to the power supply. To go at higher and higher speeds it takes more signal conditioning. These days many PHYs dynamically change their parameters to better send and receive signals and using those features can use significant current. The Regen tries to take on the work (with the resultant changing current draws and resultant noise) on the input side so the DAC's PHY doesn't have to and then the Regen sends a much more consistent quality signal so that the DAC doesn't make noise in itself trying to accommodate a signal that's changing quality.
Like jitter it's another way that a relatively little known effect can end up being manifest noise.
I cannot tell you with any honesty that what I was listening to is in any way better, worse or the same as these other USB devices: the Jitterbug John Atkinson reported in print, Michael Lavorgna and John Darko on the web, or the Uptone Regen, or Schiit Wyrd, but from all accounts, adding one of these devices can bring wonderful improvements for little money.
The technology I auditioned last week set me on my rear and removed my socks in one swell foop. Easily as big as the difference between a S/PDIF input and the Network Bridge and perhaps even bigger. I haven't yet taken measure of the size, but oh my gosh, this requires more investigation and, perhaps more importantly, it shall never leave my system, despite the fact I haven't much need of longer USB cables. Perhaps most significant to me is the nature of the change itself: simply ground breaking. As I wrote yesterday the new USB interface removes whatever was blocking the three dimensional origami shapes of instruments in the music.
I have never heard anything quite like it.
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