jksbt wrote: > Hi, > > I'm new to these forums but have really learned a lot from them. Triode > your applet works for peachtree idac although the dac uses an adaptive > usb 1.0 and so sounds better using the coax from the sbt. Very easy to > use and I appreciate all the effort you put into it. > > I have used some of soundcheck's suggestions (quite helpful) and your > edo applet and could definitely notice a significant improvement in SQ. > Thank you both. > > I had an idea to greatly reduce the jitter of an sbt that entails > modifying your applet ( or maybe it doesn't?). This might not make any > sense so please feel free to throw darts or whatever at this idea. In > my situation and possibly others here, the sbt is not close to the > pc/nas setup. Perhaps 20 or 30 ft. I just run a long cat 6A eithernet > cable (thanks soundcheck--it does make a difference although I can't > believe I am saying that) from my pc to the sbt. Then I could go to the > dac via either usb or coax which is a short 1m cable. Given the jitter > in the sbt is good but perhaps not as good as we all might like I was > wondering if the following idea is feasible: Could you use the usb > output of the sbt (using some version of the edo applet) to go to a low > cost usb to spdif box that would clean it up significantly and avoid > making any hardware mods to the sbt (thereby avoiding violating the > logitech warranty). The output of the spdif box goes into the coax input > of the dac but now the jitter of the sbt has been greatly reduced > (hopefully) and no one has to mess with hacking into the hardware > innards of the sbt. Although if that is your thing then more power to > you. > > I read from triode and John Swenson's excellent and well thought out > explanations that the edo applet may not be able to do this currently > because it needs to query the dac to help set up the usb output channel > in the sbt. I suppose a usb to spdif box in between is going to make > that impossible. However, maybe a simpler usb 1.0 pass through version > (or applet option) of the edo code would work to accomplish this? An > added bonus is that this would make the edo code even more versatile > since their would not need to be a dac query. Thus, the concern about > making it work with various dac brands would be avoided thereby creating > an even larger user base for this mod. Although it does increase the > cost to buy a usb to spdif box. Or maybe I have no idea what I am > talking about (quite possible). > > A question one might ask here is why not go directly from the pc to the > dac via usb? I have tried it and I can tell you that long usb cables > are not OK for transmitting high quality audio. Many dac mfr's warned > me against it and they were completely correct. The sound degradation > was obvious and not pretty. On the other hand ethernet is adept at > traveling long distances and does possess transformer isolation at its > receiver. So what I am attempting to do is transmit to the sbt as > cleanly as possible over longer distances using ethernet and then > reducing the sbt jitter with a usb to spdif box (with short 1m usb > cable) and then go to the dac via spdif coax (again short cable). > > Would appreciate any comments, etc. on this idea.
In the case of a USB to S/PDIF converter the specs of the converter itself are what the Touch will send to the server, S/PDIF if unidirectional, there is no way the Touch can query a DAC over an S/PDIF link. On your main question, unless you spend a lot of money on the USB to S/PDIF converter (ie get a really well implemented asynch USB interface) it is most likely not going to have as low jitter as the Touch does already. Now there is a whole different aspect of S/PDIF interfaces called impedance matching. The spec calls for 75 ohms for the source, receiver and cable. The cable is the only part that usually comes out close to 75 ohms. Most transmitters and most receivers come nowhere close to 75 ohms. Even the cables very rarely have 75 ohm connectors. The differences between source and receiver are what causes the problems (I don't have time to get into why that is). So even if both are not 75 but are close to each other you can have a decent link. So say if both the source and receiver are near 50 ohms and you have a pretty close to 50 ohm cable, this part of the equation will be good. Unfortunately there is no way to know what a particular Source or DAC is, you just have to try things and find pout what works best. In a lot of cases someone will say "this is a really good source" when in reality its nothing special, it just happens to match the DAC they are using, for someone else with a different DAC it might be terrible. And also to confuse the issue DACs vary greatly in how much they are sensitive to these effects, some are quite sensitive and some are fairly insensitive. So for some all these sorts of things do make a significant difference and for others all this stuff is almost irrelevant. So IF you have DAC which is sensitive to this stuff both the inherent jitter of the output AND the impedance match between source and DAC come into play. The Touch has pretty good jitter level as is, certainly not the best on the planet, but quite good. Its a total crap shoot as to whether its going to be a good impedance match to any particular DAC. Compare that to a USB to S/PDIF converter, very few inexpensive ones even come close to the jitter level of the Touch. You usually have to spend quite a bit to get one that has significantly lower jitter than the Touch (and I mean quite a bit more money than the cost of the touch itself). They DO exist, but not inexpensive which seems to be part of your inquiry. And then you have the crap shoot of impedance matching all over again. So you could have a situation where the Touch is not a good impedance match with your DAC and you find a USB->S/PDIF converter that is about the same jitter as the Touch but just happens to have a good match with your DAC and it sounds better. You could also find a really good converter with very low jitter, which has a poor impedance match with your DAC and it sounds no better than the Touch. The Touch may have a good match with your DAC and sounds better than any of the converters, even the really good ones. You really don't know what the situation is going to be until you start trying things. In my opinion the best way to go is get rid of the S/PDIF part of the equation all together and get a GOOD DAC with a really good asynch USB receiver, connect it to the Touch with a fairly short cable and let the ethernet cable to the touch be your long connection. If you do that you get rid of a LOT of the "you take your chances" aspect of dealing with S/PDIF. BUT you have to make sure you don't get a DAC with a proprietary USB implementation such as the M2Tech ones. A numbers of companies use the M2Tech OEM board in their DACs, you can't use those with the Touch. I know it's not as cut and dried as you would like it to be, but unfortunately that's the way it is. John S. ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=94512 _______________________________________________ Touch mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/touch
