USB Regen from UpTone

[Antoine]

Me to

The measurements will be even more interesting!!!

Not at all, as he's "measuring" the wrong things...

Here's a reaction to this "test" by Alex Crespi, owner of Uptone Audio.

Dear Mr. Walrdrep:

I am the owner of UpTone Audio LLC, and thus the producer of the USB REGEN (designed by my associate, the well known John Swenson). I have followed off and on your conversations with Michael Lavorgna and your postulations about what the REGEN does or does not do. Now that you are about to “test” one for yourself, it seem prudent for me to make a few comments in advance:

1) As an industry professional with a web site and readership, it seems highly irregular and somewhat unethical for you to engage in a supposed objective review of a product (your bias and preconceived notions aside) without contacting the manufacturer (me) to ask permission or a single question about design or use of the device.

2) I can tell you right now that you will not measure any difference in the bits, and if that is, as you have stated, your only criteria for judging the efficacy of the device then you are wasting you time.

3) Despite M. Lavorgna imploring you to read the condensed “white paper” of ours (published at the front of the AudioStream review of the REGEN: http://www.audiostream.com/content/upton...-usb-regen) you continue to misconstrue the mechanisms by which the REGEN works (improving signal integrity at the input of the DAC so that the DAC’s PHY chip leaves its pre-processing circuits off, thus generating less ground-plane and packet-noise and fewer current/voltage spikes on the PS).

4) Surprisingly, you also seem to mis-understand asynchronous DAC clocking and the role (or lack thereof) played by the 24.0MHz USB clock. The clocks running the hub chip and PHY in the REGEN and the same function clock (typically 12Mhz or 24.0MHz) at the USB or Ethernet input of a DAC have absolutely no relation to the DACs master clock(s) or jitter developed inside the DAC. And NEVER do we claim the REGEN delivers a “lower jitter” signal to the DAC.

5) If you would study the chips and input architecture common to all USB-input DACs, you would understand that what is input to these stages is not bits at all, but high-frequency voltages with variations that must be decoded. First by the PHY chip (a nasty beast with several PLLs and internal clocks at various phases), and then by a MAC USB protocol engine (in an FPGA, XMOS, Cmedia or other custom chip). And it is here where jitter and pernicious ground-plane noise starts. All the isolators and reclocking flops in the world can’t keep all of that from reaching the master clock. The place to measure jitter is at the input of the DAC chip, but I am certain you are not set up for that.

6) If you wish to see tangible evidence of the effect the REGEN has on signal integrity, then you will have to get yourself a 3-4GHz scope and set up for eye-pattern testing. John Swenson has done just that, and we will soon publish such measurements showing the functioning. Yet just this morning someone sent me a link to post where well known engineer John Westlake (late of AudioLab) ran an eye-pattern test on a USB signal without and with a REGEN. He posted the graphs and talks a bit about what he saw:
http://www.pinkfishmedia.net/forum/showt...ost2680112

7) The REGEN works the same for DACs from modest to extreme. If one can hear even a slight difference with a USB cable feeding your DAC, then you should hear an even bigger difference with the REGEN–if properly used. To maintain the improved signal integrity and impedance match, the REGEN should be positioned at the input of the DAC by use of the solid USB male/male A>B adaptor provided. Putting a USB cable after the REGEN will reduce–but not eliminate–its effectiveness.

8) While you may consider the Benchmark DACs high-end (and thank goodness they finally moved away from the ASRC of the earlier models), they are decidedly very much in the low-to-middle range of DACs our customers are successfully using the REGEN with. Some of our clients are using reference-level DACs from Berkeley, dCS, PS Audio, exaSound, Meitner, MSB, Resonessence, Auralic, and Schiit just to name a few.

9) I agree that the bits are the bits. But they are not bits until they are turned into such–and THAT DOES NOT HAPPEN UNTIL THE OUTPUT OF THE DAC’s USB INPUT STAGE.

So please do your readers a service and skip trying to measure data differences that I can tell you right now won’t be there. And the trouble with trying to measure the analog output is that the ADC chips of the measurement gear are going to obscure the nature of the improvement as well. That’s a whole other argument and controversy that could on ad infinitum, but even if you measure analog variations (the magnitude of what so many hear with the REGEN really ought to be measurable), how to correlate those to qualitative differences is a separate challenge.

My telephone number is on our website and messages via the contact page come directly to my e-mail account. I trust you will show integrity in performing your evaluation and that you will lend an open ear and mind as well. The REGEN is not “snake oil.” It is solid engineering to addresses a very real issue limiting the sonic performance of the USB interface.

Sincerely,

Alex J. Crespi
UpTone Audio LLC