Guess I should explain jitter for grins and cause I'm bored :P A DAC receives a serial stream of data. Just one's and zeros:
1001100111001 The catch is that there is no clock in that data. There isn't a seperate line saying "okay, here comes the next bit!" which would get rid of the jitter argument completely. And because even the crystals that control timing are not -exactly- accurate, you can see errors where it tries to derive a clock. If the sender is sending bits at 44,100 bits per second, and the receiver's clock is just a slight bit off at 44,098 bits per second, it is going to misread some. The Toslink vs coax argument boils down to whether the impedence and noise of wire introduces bit errors or if the conversion from electrical to light to electrical creates timing and bit errors. They both do, actually, the question is which is more noticable which gets into lots of variables as well as psychology. A hard drive doesn't (assuming it works) have that problem: it has external timing. In addition to the 8-64 bits that it transfers at once (oooold MFM drives like the ST506 transferred 8 bits at a time but they haven't been used on PC's in 20 years), there is a "okay, the data bits are valid ... NOW!" bit which is set when all the bits are driven properly on the bus, so the controller knows that it can read them. Timing isn't an issue: which is why you don't have to swap hard drive controllers when moving from a slow 3600rpm drive to a 7200rpm drive or faster. The timing is delivered with the data. The only thing you'd notice when swapping between fast and slow drives is that the disc is either faster or slower... the bits would still be the same. (And even a slow hard drive is fast enough to drive 44.1kbps.) If the controller had to guess at the timing, like it does with Toslink or coax, then you would be having jitter problems, and would have to match your hard drive to your controller. You would even then still have errors: you can never make them guess exactly right unless they share a common clock. Jitter problems are basically a design flaw of how digital interconnects work in Audio. The people designing digital audio connections didn't think it matters, that your brain would cover up any problems (which it often does do or stereo wouldn't work). "Close enough" works in audio (how close "enough" is another question), but not for data on a hard drive where a single bit of corruption will lead to lost data. -- snarlydwarf ------------------------------------------------------------------------ snarlydwarf's Profile: http://forums.slimdevices.com/member.php?userid=1179 View this thread: http://forums.slimdevices.com/showthread.php?t=24616 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
