The defintion of transport (what is a transport btw?) and DAC is IMO already confusing and misleading and IMO cannot be discussed as such.
What counts is the entire "digital path" with all its building blocks. And there are many players in the game. That digital path you'll find on the commonly called "Transport"-device AND "DAC"-device. The digital path ends right at the actual DA converter chip or better at the point where the digital data gets converted to analog. Modern DAC chips e.g. ESS Sabre extent that external digital path even further by adding some more internal digital path related building blocks. The entire digital path you can consider the "transport layer". It all acts as a "transport". Everything on that digital path can cause distortions such as jitter, noise, EMI/RFI, drifts asf. Distortions ususally are of cumulative nature. Of course there are building blocks to reduce all those distortions. But e.g. even ASRCs are not jittefree. Even high precison clocks do show variations, because of e.g. thermal drifts and powersupply variations. Most reclockers get rid of some distortions at least. Some building blocks are "interface" related, some of them are "stream quality" related. SPDIF is known to be a pretty poor interface building block on the digital path. It is chosen by manufacturers because if its simplicity and lack of economic alternatives. SPDIF comes with several known flaws. (We don't have to discuss this again). It is a consumer audio interface. Asynchronous USB interfaces are a nice alternative to SPDIF. Not perfect but usually better then SPDIF. The point is, even though the Touch comes with an USB interface,it would have been impossible for Logitech to declare that USB interface a SB Touch audio interface. That might have been the better choice on the performance scale. However. Logitech would have been relying on Linux USB-DAC drivers. And that's would have been a major problem. Popular devices with propriatry drivers just wouldn't even work. All the digital path impact would become irrelevant if the industry would manage to properly decouple and reclock the incoming stream from the DAC stream right in front of the DA conversion stage assuming the bits and words would arrive at that point "bit" and "word" perfect. And alternative solution is shown here: 'I2S interfaced and clocked slaved SB Touch' (http://forums.slimdevices.com/showthread.php?t=83138&page=2) . This solution is even bettter than word clock synced solutions as they are widely used in the pro-audio scene. That solution just lacks galvanical isolation. My Touch Toolbox, which lowers those cumulative distortions on that digital path to a certain extent, would be obsolete and not show any differences if the downstream digital path would be done right. Cheers -- soundcheck 'soundcheck's Touch Toolbox 2.0' (http://soundcheck-audio.blogspot.com/2011/01/soundchecks-squeezebox-touch-toolbox-20.html) || 'soundcheck's Touch Toolbox - Beta Blog' (http://soundcheck-audio.blogspot.com/2011/01/soundchecks-tt-beta-blog.html) ------------------------------------------------------------------------ soundcheck's Profile: http://forums.slimdevices.com/member.php?userid=34383 View this thread: http://forums.slimdevices.com/showthread.php?t=84903 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
