Analog Video Synth

I’d call this more of a video mixer with audio inputs, but it’s an interesting way to hack video signals. [brian] sent in the VS001 Analogue Video Mixer. He noted that it’s along the same idea as the Mac SE/30 visualizer, but outputs VGA and can route signal through audio gear for even more interesting permutations. It looks like all the information is there if you want to build your own.

10 thoughts on “Analog Video Synth

  1. 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:

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

  2. 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!!

  3. 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.

  4. 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?

  5. 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
    and you will read about it and the incredible special effects it could produce.

  6. 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:

    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 3×3 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.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.