外接時鐘

Basically, the accuracy of a clock, meaning what time is it, in, say, 100 years, is actually not very important. What really matters is the short-term stability of the clock, generally described as phase noise. For high-quality clocks, the phase noise over a particulat bandwidth, say 1 Hz to 100 kHz, will be in picoseconds, possibly femtoseconds. Jitter is another way of expressive phase noise. Very low frequency phase noise, from 0.1 to 1 Hz, seems to be very important for realism, presence and soundstaging.
Most USB-S/PDIF interfaces don't even have published phase noise or jitter specs, which often relates to the fact that their performance in this regard is poor. Rad the reviews in Stereophile and 6moons. Often the designers don't have the equipment or technical knowledge to make sure measurements in the first place. Until quite recently, good phase noise analyzers cost from $40 to $100K and up.
Using an excellent external reference clock may improve the performance of even high-quality DACs which have a word clock input. In addition to the Grimm CC-1, the Black Lion Audio Micro Clock MK2 has very good phase noise measurements.
So you're asking exactly the correct question: Why are clocks important, and how does one evaluate them? This is a beginning. If you check Wikipedia, there are some good discussions about phase noise and jitter.

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出處 http://www.computeraudiophile.com/co...#comment-88545

簡而言之, 穩定性比準確性重要, 穩定性也就是所謂的Jitter, 其中也提到 0.1到1HZ超低頻的準確性對音場等有很重要的影響 (這一部分我不知道原因)

所以以後不要被文宣給誤導了, 一百萬年誤差一秒也不一定就適合啦~~~