There are two major "camps" with regard to digital audio optical cables, single fiber and multi-fiber. Why the difference?
The traditional optical cable uses a large (at least in regards to a wavelength of light) single plastic fiber. This means that light rays entering the fiber at different angles can take different path lengths to get from one end to the other. With such a large fiber light rays take a zig-zag path down the fiber. One that enters parallel to the fiber will have few zigs and zags and a ray thet enters at an angle will have more zigs and zags. These add up over the fiber length producung rays that take different time delays through the fiber. This causes "edge smearing" at the receiver. An attempt to fix this was the multi-fiber bundle. In this apprach each fiber is vastly thinner so its internal dimensions are on the order of a wavelength of light, thus there is no zig-zag, the delay time through the fiber does not depend on the angle of incidence. So why the bundle, why not just one? The optics at the transmitter and receiver are designed to send the light into a certain sized fiber (the large plastic one), if you use just a single very thin fiber almost none of the light will actually hit it and there will not be enough light at the receiver to trigger the light sensor. So they make a bundle of thin fibers that is the same size as the single large one. There is also the material used, the original spec was plastic, because it bends. Glass at that thickness would break not bend. BUT glass at very small diameters IS flexible. Traditionally the very thin fibers were made from glass because it was easier to make thin glass than thin plastic. Now they have figured out how to make plastic fibers thin as well as glass. So now you can find single large plastic, multiple thin glass or multiple thin plastic. The plastic and glass cables DO have different optical properties, I'm not an expert on this but listening to a real expert I got the impressionthat that for the short links that we are using the plastic might be better. I have used a single plastic and multiple glass cables and found that the multiple glass ones almost always sound better than the single plastic. You can get them for $30 or so, so its not that big a deal to just go with that. I have not tried the plastic multi-fiber cables, some that have prefer it to the glass ones. The multi-fiber plastic cables are much harder to find and more expensive (but not hugely). Now as to differences between optical and coax, its a crap shoot. The common optical receiver modules are not all that great, they are fairly noisy and have very low bandwidth, both of which can significantly increase jitter on the recovered signal. Whether this is going to affect the jitter at the DAC chips depends very much on the receiver circuitry. Coax if done very well should be better, BUT very rarely is it done very well. The jitter at the reciver depends both on the inherant quality of the source transmitter (jitter, noise, risetime etc) AND on the reflections caused by impedance mismatch. The output impedance of source and the input impedance of receivers varies from about 35 ohms to about 120 ohms. There is no way to tell which is which, price or "reputation" is NOT an indicator of what its going to be, the units out there in the wild are all over the map. The result is that its a crap shoot as to what you get. If you get lucky and your source and receiver are close to each other (note it doesn't have to be both at the spec value, just that both match) your coax probably will sound better than optical, if they don't match the optical will probably sound better. The result is that in reality there is no way to tell which will sound better, try both and choose which sounds best. If you find that optical sound best then you might want to try different optical cables, in particular try a single plastic and a multi-fiber glass or plastic one. If both coax and optical sound identical with basic cables you can try different cables and you might find that now one sounds slightly better than the other. My experience is that digital cables DO sound different, but that price has nothing to do with it. I have tried expensive cables and they don't sound any better than some of the inexpensive ones. Others have found different. My best sounding coax cable is one that came free with a DAC many years ago. Again it probably has more to do with matching the impedance of your equipment rather than any inherant "goodness" of the cable. For example if you get lucky and you have a source and receiver that are both near 90 ohms a 90 ohm cable is going to sound better than a 75 ohm cable. So try a bunch of stuff and determine what sounds best to you. If you can try expensive cables on loan or a friend's etc go for it, it might be better than anything else, in which case you have to decide if its worth it. But if you try enough you will probably find a less expensive one that sounds as good. The best advice I can give is "don't take anybody elses opinion as gospel", there is such a huge variation in equipment so that what sounds the best to one person is almost guaranteed NOT to be the best for you. You HAVE to do the testing for your self with your system. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=90211 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
