On Sun, 2002-06-16 at 15:21, Sellam Ismail wrote:
>
> This has always been an area of confusion for me. Can someone recommend a
> good reading that will explain video as far as composite vs. RF and
> modulation and all that?
I can't provide a weblink, but i'll explain it as how I think of it.
Composite video carries a video signal much the same as a speaker wire
carries sound. upper and lower voltage leves are set to correspond to
full brightness and full darkness. There is a level outside this range
called "blacker than black" which is used to indicate a frame sync or
line sync pulse (i'm sorry but I cannot remember the levels at this
point in time - IIRC whit is about 4v black is around 0.7v, blacker than
black is lower than this. (please correct me nicely))
RF is the modulation of this onto a radio signal in the same way that
the sound output from a radio station is modulated onto onto a radio
signal - they are just at different frequencies.
Modulation is the act of using a low-frequency signal (the video or
sound input) to modulate a much higher carrier frequency. There are two
major types of modulation - AM and FM. In AM the input frequency
modulates the amplitude of the carrier wave - an spike on the input
signal would make the carrier frequency appear 'louder' to the reciever.
In FM the input wave shifts the frequency of the carrier wave slightly.
In both cases if it were humanly possible to listen to the modulated
signal (audio or video) it would be garbage - either a single tone that
would wobble in amplitude or vary slightly in frequency. In each case
the modulated signal needs demodulating or decoding to reproduce the
input signal.
*runs and hides under a rock* i'll shut up now, promise.
Alex
--
Live like you will never die, love like you've never been hurt, dance
like no-one is watching.
Received on Sun Jun 16 2002 - 09:55:58 BST