jkeny wrote: > As I said I already corrected both you & Arny, a number of times, 'here' > (http://forums.slimdevices.com/showthread.php?103684-uptone-audio-regen&p=819127&viewfull=1#post819127) > & 'here' > (http://forums.slimdevices.com/showthread.php?103684-uptone-audio-regen&p=819129&viewfull=1#post819129) > "Similarly, Archimago might care to answer why he wants to borrow a > Regen, to measure it's reduction of the 8KHz spike when this is not the > target of the device? > A typical red-herring measurement, as per usual." > > I would like to see the context of that - he's not talking about the > Regen - here's what he plainly says about the Regen which I already > quoted to you/Arny in the links I gave above "-"This packet noise > consists of two parts: noise from the USB protocol engine and from the > USB PHY. The protocol engine noise does not depend on the input signal > quality, just the data, so its impact is always going to be the same no > matter what is done with the input. -*The PHY is the part that actually > connects to the electrical signals on the bus, ITS contribution to > packet noise IS dependent on the quality of the input signal. > _This_is_the_part_the_REGEN_targets.\"_* > > So you are going to persist in focussing on the 8KHz packet noise & > measuring for this - a noise which isn't being attenuated by the Regen, > simply because you don't understand what the Regen is purported to > address? Surely measurements are meant to uncover the efficacy of a > device in it's purported operation? If you can't think of a way to do > this measurement, that is no reason to do some other irrelevant > measurement & pretend that it measures the efficacy of the device.
OK. Suppose we take 'Swenson's comments here at face value' (http://uptoneaudio.com/pages/j-swenson-tech-corner): 1. There is an 8kHz burst due to packet noise. 2. This is "strong" and in the audio band. 3. This noise goes everwhere! "This noise can cause jitter in clock oscillators, reclocking flops, and DAC chips. It can also go directly into noise on the output of DAC chips". "well what about the DACs that have full isolation between the USB system and reclocking on the DAC side? Unfortunately this noise likes to make it through even this." 4. He distinguishes between "protocol engine" and "PHY" noise with the PHY component causing the bus connection noise: "The protocol engine noise does not depend on the input signal quality, just the data, so its impact is always going to be the same no matter what is done with the input. The PHY is the part that actually connects to the electrical signals on the bus, ITS contribution to packet noise IS dependent on the quality of the input signal. This is the part the REGEN targets." 5. Signal Integrity is what worsens the PHY noise: "When the SI is very good, the PHY can turn off the pre-processing steps and easily determine the bits. As the SI degrades the PHY turns on different parts of the pre-processing as needed. Each of these steps takes a fair amount of power to operate, thus creating noise on the power and ground planes. The more processing the PHY needs to use to determine the bits, the more noise is generated. Thus part of the packet noise is directly related to the signal integrity of the incoming signal. The higher the SI, the lower the noise." 6. -He then makes some kind of strange logical shift:- "It is very important here to realize this is noise that is GENERATED inside the DAC by its own operation, it is NOT noise on the USB bus that is somehow getting into the DAC as is commonly thought." HUH? But you just said this noise goes everywhere?! Even making it across DACs with isolation. (Point 3 above.) And didn't you say there's a bus connection, so isn't the nasty noise created by the noisy USB PHY in the computer side what you're really worried about rather than presumably better components in the DAC? 7. So how can you make an argument that it's the portion just inside the DAC that's at issue? "The result is that the PHY in the DAC doesn't have to use any of its pre-processing arsenal so the packet noise is as low as it is going to get. Note: it does not get rid of the packet noise altogether, it is just as low as it can be." 8. Finally, to put the Regen between the computer PHY and the DAC PHY is useful in what way if the Regen itself adds a bit of noise: "The hub chip inside the REGEN has its own PHYs, which themselves generate packet noise on ITS power and ground planes. I have worked hard to minimize this noise, but it is still there. The result is that the REGEN itself is also sensitive to the SI of the signal fed to it, which is why USB cables on its input still make a difference." Here's the problem with Swenson... He's never really clear. Just hand-waving and innuendos as suggested by Arny. The only thing we're clear about is that there is this packet-noise and a substantial portion of it is 8kHz, and potentially audible as I measured. This noise goes all over the place as he says but then reduces the Regen to its ability to -maybe -reduce the noise portion generated by the DAC's internal PHY if we even assume he's correct that the Regen actually improves "Signal Integrity" and this actually does much to the PHY noise in the DAC itself. How do we know he's right? Again, this is noise, where are the measurements before and after adding the Regen to the USB chain? Like I said, without this demonstration, this is all hypothetical and I am concerned about that Point 6 which suddenly seems to just claim that the DAC PHY noise is somehow the problem (ignoring that the computer makes noise and even the Regen adds to it). Heck, how do we even know that the noise isn't made worse with the Regen in place since it uses a "a common USB hub chip". So, jkeny, please tell us plainly and help me "understand what the Regen is purported to address". Archimago's Musings: (archimago.blogspot.com) A 'more objective' audiophile blog. ------------------------------------------------------------------------ Archimago's Profile: http://forums.slimdevices.com/member.php?userid=2207 View this thread: http://forums.slimdevices.com/showthread.php?t=103842 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
