[music-dsp] Re: video > audio channels
James Chandler Jr
jchandjr at bellsouth.net
Wed Apr 11 16:25:56 EDT 2001
> >i sit possible to effect video by using audio filters?
> >for example:
> >video input (composite video) > digital delay pedal > video output
> >(monitor / projector / camera
> >by using delay would you get a time echo effect? and what about other
> >filters? phase and flanger? pitch shift?
Am not very expert on video, but here are some dumb opinions.
If remembering correctly, I think NTSC bandwidth is something around ten
MHz. That's fairly low for video, and is the reason that NTSC monitors are
too fuzzy to display much more than 40 characters per line. Analog NTSC
video monitors will low-pass info above their specified bandwidth, which
blurs fine detail (but also avoids video aliasing).
I think you could use a faster version of an audio digital delay circuit, to
delay NTSC analog video. It would need a bandwidth up to 10 MHz or so (I
If you want to add regenerative feedback or "pitch modulation" as used in
audio delay effects, it would get trickier.
An NTSC composite signal has a "sync pulse" and a "color burst" signal at
the beginning of each line of video information.
Each line's waveform begins with the sync pulse and color burst, which
allows the monitor to lock up to the input signal. After the line-start
markers, follows the analog squiggle which represents the brightness level
of that line of video.
Fancier than simple delay, anything you do to the video, would require you
to strip off the sync info, mess with the line info, and then merge the
changed line info back with the sync info. If you don't preserve the sync
info, the picture will roll and tear.
It doesn't take a lot of circuitry to strip off the sync info. Any of the
little home-user video regenerators, titlers, or faders that sell as cheap
as $50, have sync circuitry in them.
There used to be copious do-it-yourself info about building simple video
manipulation boxes, in mags like Radio-Electronics, Popular Electronics,
etc. But I think most of those mags are long-gone.
James Chandler Jr.
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