Comments on: Analog Video Synth

By: tim musabay

tim musabay — Tue, 11 Mar 2008 13:44:48 +0000

man…..this is amazing….if only i had the technical ability to do this myself i would….

if the person who made this is reading….AMAZING WORK……
i doubt you would commission such a device but if for some reason you would please write me at wildturkey1978@hotmail.com

By: pixel form

pixel form — Wed, 19 Dec 2007 18:40:07 +0000

I've been experimenting with hacking the VGA synth and have been in contact with Brian about his work. From email correspondance and jpgs of his circuit diagrams, I have determined that a great deal of generating the "beams" (vertical oscilloscope lines) was intuitively figured out. He started with a VCA circuit and used that to control the logic chip circuits used in tampering with the VGA synch signals. The diagram he sent me was a "snapshot" of his breadboard after working the modded VCA circuit into his logic system. II have had mixed success in producing a VGA synth of my own. The page outlining my work is being migrated along with the rest of one of my sites but I still have a video available:

http://www.art-rash.com/pixelform/video/apeiron-peras-i-comp.mov

The vertical banding is generated by driving 40106 based schmitt trigger oscillators with the hsynch. A tunable resistor allows subharmonics of the Hsynch to be generated and thus different numbers of vertical bands.

The audio and video are together generated by a feedback network (through and audio mixer + reverb) and switched internally by a self controlled 3x3 routing matrix.

Right now I'm working on a touch based VGA synth that uses overdriven op-amp circuits to produce signals for use as video and audio. More on those experiments later.

By: Brian

Brian — Wed, 13 Dec 2006 22:20:23 +0000

The video 'synthesizer' is not a new concept or device. While at the Ontario College of Art in 1977-78, I used one, the Rutt-Etra VSynth, with audio and video signals to produce 'art' and special effects on video. The college spent a lot of money buying one but, apparently, I was the only person at the college to be able to actually produce anything more than trivial with it. Nam June Paik, a video artist, used one too. Get over to http://www.audiovisualizers.com/toolshak/vidsynth/ruttetra/ruttetra.htm
and you will read about it and the incredible special effects it could produce.

By: fish

fish — Sat, 11 Nov 2006 16:59:05 +0000

a damn cool hack.
wish i could build things like this one, too

By: cosmo

cosmo — Fri, 10 Nov 2006 23:05:31 +0000

Any chance you can post more detailed schematics?

Im not quite understanding how the audio portion is being handled, namely what is implied with the audio beams?

Wouldn't the amplitude of the audio signal vary the brightness of the pixels, but not provide the pretty vertical waveforms shown in the screenshots? Are you somehow delaying the pixel data accross each horizontal scanline?

By: bbb

bbb — Fri, 10 Nov 2006 19:33:54 +0000

well it works on some lcd gear but not on some others…
actually the one projector it didn’t work on could be tricked into working a bit, but not stable enough for super freakie changes in the video.

the solution (well a solution) was a 4066 controlled by the h and
and v sync to get the blank areas back. this made the rgb signals a bit too dim… some 2n3904s made short work of that but… they boosted the contrast too much for my liking. highspeed op amps are the ticket i think. and a bit of agc i guess…. but all that extra stuff can just go in a little box stuck on the output for use as need.

By: lain

lain — Fri, 10 Nov 2006 15:12:23 +0000

vga is actually a pretty simple system, there's two sync signals (hsync and vsync), which are active low. then theres the analog R, G, and b signals.. from what i understand the vga spec calls for 0.7volt max for the rgb signals to indicate full brightness, and lower the voltage will control brightness/intensity. a pulse on hsync indicates the start and end of a line, and a pulse on vsync indicates the start and end of a screen,.

so, one fullscreen image would involve a pulse on vsync, then a series of pulses on hsync indicating the start and end of each line, then another pulse on vsync. timing depends on the pixel clock which is determined by the mode (vga, xga, etc.)

there is also the "front porch" and "back porch" which are areas where all rgb signals are blanked out and the sync signals are not pulsed, this is the time when the deflection coils in a CRT jump to the start of the next line (the time between the starting and stopping hsync pulses for each line). there is also a front and back porch for vsync, allowing it to jump back up to the start of the screen..

thus, hsync controls the frequency at which lines are drawn, and vsync controls the frequency at which entire screens (frames) are drawn.

he mentions it doesnt work on an lcd, that is likely because he doesn't seem to have any circuitry to protect the front and back porch signals. if he could keep these intact, it would perhaps provide a slightly less 'awesome' image (it wouldnt fluxuate the screen so much, because the deflection coils wouldnt be going all whacky), however it would then make it compatible with the adjustment feature in lcds.

just thought i'd share that since i recently started working on a digital KVM-like device and i've had to digest all this, myself! friggin cool hack!!

By: wolf

wolf — Fri, 10 Nov 2006 06:38:40 +0000

Did anyone else notice the internals? I gota hand it to him, thats the true hacker approach to wiring

By: Enrico Fermi

Enrico Fermi — Fri, 10 Nov 2006 05:12:13 +0000

from what i can see from the diagrams he has the red green and blue signals from the VGA being sent to some logic that plays with their syncs. After the logic part (he just labeled it as logic gates, counters vibrators, etc), the audio is mixed into the red green and blue signal lines.
this diagram is kinda hard to find, so i'll put up the url:

http://www.mediumrecords.com/random/wp-content/vidisynth/vidisynthVGAtap.jpg

i'm not an expert at this, but i hope this will help some.

By: Corwin

Corwin — Fri, 10 Nov 2006 00:57:35 +0000

Wow, a circuit bent vga signal. Wish there were some schematics. Given the diagram though, someone ought to be able to hack a similar device together.