什么是clockjitter
5.7 - What is clock jitter?
Clock jitter is a colloquialism for what engineers would readily call
实训体会time-domain distortion. Clock jitter does not actually change the physical content of the information being transmitted, only the time
at which it is delivered. Depending on circumstance, this may or may not affect the ultimate decoded output.
Let's look at this a little more cloly. Digital audio is nt as a
t of 1's and 0's. But that is only a logical
construct. In order to transmit binary math electrically, we u
square waves. Realize that although we have two mathematical states, we have to transmit such a construct using control voltages and comparators.
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All digital audio systems start with a crystal controlled oscillator producing a square wave signal that is ud to synchronize the entire digital audio sampling and playback process. Now, for a clock, we don't really care about the fact that the clock might be at state 1 or state 0 at any given moment. That doesn't give us any information.
As a computer, I can't tell if my clock has just gotten to state 1, or
所有的福字if it's been sitting there for a microcond. Thus it isn't the
居里夫人的简介states we care about. Instead, we care about the state
黑暗之中
*changes*....when the clock shifts from one state to the other.
Now, in a perfect square wave (no such thing exists), the change of state would be instantaneous. it's done. But in reality, it doesn't work this way. Square waves contain high orders of harmonics. Fourier teaches us that all complex waveforms are made up of simpler waveforms. Thus, as we run through noisy electronics, long cables, inadvertent filtering circuits, we begin to lo some of our harmonics. When this happens,
电磁炉出现e0our square wave begins to lo form.
The result of this is that our nice sharp corners become rounded. So
our state changes are no longer precily at the edge anymore, becau there is no more edge. The pointy edge is now all fuzzy. It now depends on design of the electronic comparator circuit as to when the clock state will change, as the stage change has shifted. The clock
is, esntially, jittering.
People love to bark out "Bits is bits. A copy of a computer file
works as well as the original." Yes, this is true. But the双燕离
jittering bits can create audible distortion during the digital-to-
analog conversion, and the industry is working hard to reduce the amount of jitter prent in digital systems.
Furthermore, emerging rearch is suggesting that certain types of
jitter may produce digital copies with eccentricities that result in
more jittery output on playback. The jury is still out on the
脑血栓后遗症specifics however. Stay tuned. [Gabe]
