[Czilla9000]

What really causes Jitter, or do we not know. If so, why does vibration dampening help.


I need to know for a physics project (those of you from the DIY forum know what it is).

 

[Czilla9000]

I know jitter is caused by timing errors. But how does vibration cause timing errors?

 

[taoster]

crystals and jitter-bugs

 

[planar]

vibration causes CD drive to fix up the "gap" by re-read the data portion affected by the vibration. Such process will generate some timing difference to the timing of overall signal stream - that is jitter. So less vibration will cause less reading error, the CD drive needs less time to fix up the error so data stream will flow more effortlessly (or steady).

For example, if you are writing something on a bus, the more the bus vibrates (or shakes) the more difficult for you to write properly and that will decrease your writing speed because when it vibrates, you would need to fix up the bad writing cause by the vibration. So the speed of your writing (eg one word per second) will be affected by your effort to combat with vibration. This will then affected the "smoothness" of your writing speed - that is jitter in real life

 

[lan]

Well vibration is only on the transport end. In transmission, electrical variation going to the DAC, EMI on the coax cable, refraction errors and laser "weakness" on the optical cable can cause more jitter.

 

[dvw]

czilla9000;

You'll need to define your question more precisely. I assume you are talking about clock jitter.

In order to understand jitter you'll need some semiconductor knowledge (you are talking about Physics project, right). When the transitors are not conducting, it acts like a capacitor. The variance in the charging and discharging of the junction is called jitter. This jitter in conducting is the electrical jitter.

vibration, EMI, reflection etc can cause error but not jitter.

In data transmission system, the clock is embedded in the data. PLL is used to recover the clock. The transition of 1 to 0 is important for the PLL to work correctly. Depends on the line code used, there could be trade off in implementation that affects the jitter generated by the PLL. For digital audio, the line code is bi-phase. So the data pattern will not affect jitter. The dominating factor willbe dispersion of signal that causes ISI (inter-symbol interference) which in turn causes PLL to jitter.

Jitter can be a PhD project and even that is pretty narrow in scope. This might be too big a task for high school. Jitter in audio is difficult to demonstrate to your teacher. Measurement requires expensive equipment.

So, good luck on your project.

 

[Czilla9000]

I got my project back and the teacher gave me an A! Thanks guys!