[psykostx]

Jitter isn't a specific thing to be heard and picked out, it effects everthing from system stability (dropouts) to frequency balance (as you can see from the graphs on page 1 of this post, errors in transients can add or subtract significant amounts of high frequency energy). Jitter can be heard as overall sound quality. Think of a streaming MP3 on a bad internet radio station. It sounds fuzzy, scratchy, sometimes too boomy, sometimes too thin (they all sound that way on my system). That is the sound of "aliasing" a possible side effect of jitter. I say "possible" because jitter can effect everything and everything depending on the resolution of the rest of your gear, or it can do almost nothing to change the perceived audio signal (if your rig is distorting your signal even more before it hits your ears). Needless to say, jitter is a measurable real thing, though it may not always be audible, or its effects on perception predictable. One poster said that jitter ruins the stereo image. This is true provided that you have a highly phase accurate, low distortion, monitoring system. Basically, jitter is like noise or harmonic distortion, it can actually sound pleasing, even "better", but it gets in the way of the truth. You won't notice jitter outright unless you have quite a high resolution monitoring system... but everyone will notice jitter in their final mixes if it exists in their system. Its the thing that makes your mixdowns sound like MP3's before they become MP3's...it really can ruin percieved volume, depth, hell, percieved anything. That said, don't use optical unless you have a really good transmitter and receiver. Use AES/EBU balanced XLR to transfer digital signals. It really eliminates most of the jitter, no matter what clock or converter you are using.