Archimago wrote: > 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."Good, at least it seems you have _*now*_ read the material. > Now let's see if you understand it.
> 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?There is no logic shift here, except > from you. He is saying that weak/worse signal integrity of the USB signal causes the PHY in the RECEIVER to generate extra noise. This RECEIVER PHY is located in the USB audio device & shares the ps with the DAC chip & clocks & other analogue stages in that device. It is immaterial where the signal integrity issues arise from - from the computer, from the computer's USB port (the transmitter PHY), from the USB cable - the result is that a USB signal with these SI issues causes this noise which permeates the ground plane within the DAC. Have you have heard of ground bounce within IC's? > 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."Where do you think that the noise > has an effect - on the digital side of things or on the analogue side? You are still arguing from your wrong logic from point 6 > 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."By putting the Regen on it's own > PS, & regenerating the USB signal just before it enters the DAC, can hel to ameliorate SOME of the problem - not all of it as Swenson is honest enough to state > Here's the problem with Swenson... He's never really clear.I would suggest > that he is very clear in his explanation with clearly stated engineering terms. Your failure to understand what he's saying is now his fault? You still don't understand despite having apparently read what he says & my explanations of same.> Just hand-waving and innuendos as suggested by Arny.All the hand-waving & innuendo is from both of you > *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.You mean the only thing you can understand is this 8KHz packet noise > so you insist that this must be the noise. I'm sure you've heard the phrase "to a man with a hammer everything is a nail"? > 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". > > 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?Well you said > you were going to measure the 8KHz noise with & without the Regen so what would this have shown you? The Regen is stated not to do anything to this 8Khz noise. So when you return no difference what are you going to declare? Why are you bothering with this useless 8KHz measurement claim as if it is intended to prove anything? You now want Swenson's measurements produced for you so that you will then do measurements of any worth? Why? Why wouldn't we take Swenson's measurements - I'm sure he is far better at doing such measurements & has better equipment at his disposal then you > 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".Of course that is what you are concerned about - > "hammer & nail". If you do a test for the 8KHz noise attenuation of the Regen at least be honest about it & state that this is not it's purported mode off operation when you post the results > So, jkeny, please tell us plainly and help me "understand what the Regen > is purported to address". Done! But it seems that you can't understand what's being said as I already said this back in May & you still repeat the 8KHz red herring issue in July. ------------------------------------------------------------------------ jkeny's Profile: http://forums.slimdevices.com/member.php?userid=35192 View this thread: http://forums.slimdevices.com/showthread.php?t=103842 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
