rgro wrote: > For ralphpnj and others who seem to be not quite clear about what John > Swenson's approach is to the design of this device, here is his verbatim > explanation taken from the Uptone Audio website. Note that the REGEN > device only applies to a USB-connected dac and, in the end, is > purporting to attempt reduce noise internal to the dac, itself. Just > for the sake of clarity I do not know whether the premise of the problem > nor the solution actually are empirically true nor whether the result of > it all is audible to normal humans. But, at least, read the whole > explanation and get his theory right before you debate it: > > "What I have been finding in looking at DACs etc with USB inputs is that > there is what I am calling "packet noise". This is bursts of noise > caused by the USB receiver processing the packets of data. This noise > shows up on both power and ground planes. Since the rate of packets is > 8KHz there are strong components of this noise in the audio band. 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. > > The question everybody asks then is: 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. Exactly how > this works is complicated, I have written about this in the AudioStream > articles. And bits and pieces in other posts recently. The upshot is > that neither galvanic isolation nor reclocking completely get rid of it. > They help attenuate it some, but don't get rid of it. > > 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. > > A high-speed USB signal runs at 480 mega bits per second, which is > fairly high. Different cables and connectors can significantly degrade > the "Signal Integrity" (SI). SI consists of the rise/fall times of the > signal, noise on the signal and jitter of the edges. Increases in any or > all of these can decrease the SI. The decrease in SI can be so large > that it becomes difficult for the PHY to determine the actual bits. Thus > the PHY contains several methods used to pre-process the analog signals > in order to make it easier to determine the bits. Modern high speed > serial interfaces work at all because of these techniques that have been > developed over the years. > > 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. > > 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. > > The REGEN uses a common USB hub chip to create a new USB stream. I'm > calling this a regeneration not just a reclocking. Because it uses clean > power and a low jitter clock the output of the HUB has low noise and low > jitter. By making sure the impedances are good and the REGEN is as close > as possible to the DAC the rise/fall times have very small degradation. > > > 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. > > 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. > > I hope that is all clear. It is about as short as I can make it."
Thank you rgro and all of the above only adds to what I have been saying all along: that since using USB as a means of transmitting digital audio data is so filled with problems, issues and noise why do audiophiles insist on using USB when there are means of transmitting digital audio to the input of a DAC? I predict that the next big thing in high end audio FUD will be all the problems and issues that arise when using Bluetooth for streaming digital audio and all the $$$ audiophiles will have to spend to fix these issues. Living Rm: Transporter-SimAudio pre/power amps-Vandersteen 3A Sign. & sub Home Theater: Touch-Marantz HTR-Energy Veritas 2.1 & Linn sub Computer Rm: Touch-Headroom Desktop w/DAC-Aragon amp-Energy Veritas 2.1 & Energy sub Bedroom: Touch-HR Desktop w/DAC-Audio Refinement amp-Energy Veritas 2.0 Guest Rm: Duet-Sony soundbar Garage: SB3-JVC compact system Controls: iPeng; SB Controller; Moose & Muso Server: SBS on dedicated windows 7 computer w/2 Drobos 'Last.fm' (http://www.last.fm/user/jazzfann/) ------------------------------------------------------------------------ ralphpnj's Profile: http://forums.slimdevices.com/member.php?userid=10827 View this thread: http://forums.slimdevices.com/showthread.php?t=103684 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
