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August 30, 2007 12:30 PM   Subscribe


 
That was awesome. But it kind of died at the end.
posted by DU at 12:36 PM on August 30, 2007


That's a lissajous scope. We used to do this with old B&W TV sets - hook a cheap amp up to the horizontal and vertical yoke inputs. Pink Floyd's Dark Side of the Moon looked great on it before I passed out.
posted by CynicalKnight at 12:37 PM on August 30, 2007


Wow, check this out!

Maybe I'm not sure I understand what I'm looking for here?
posted by Pollomacho at 12:55 PM on August 30, 2007


Whoa. CynicalKnight, if I were to, theoretically, want to do that, what kind of google seach terms would I have to use?
posted by lekvar at 12:56 PM on August 30, 2007


A buddy of mine wrote a converter that would produce video playback on either the waveform monitor or the color vector scope. The driving animation looked noting like an image. It was funny to mix stuff into the color bars on broadcast tapes and watch the engineer's bewildered expressions.
posted by StickyCarpet at 12:57 PM on August 30, 2007


lekvar: is this what you're looking for?
posted by oneirodynia at 1:01 PM on August 30, 2007


The link is not a music visualization. They've written code to more or less encode a computer display into the audio stream that the scope draws.
posted by neustile at 1:02 PM on August 30, 2007


Hah, this is full of old demo scene inside jokes. Metaballs, Sierpinski Gaskets, oh my!

I'm not clear at all on whether the visualizations are being generated by the same audio as is audible on the track, simultaneously.
posted by Skorgu at 1:05 PM on August 30, 2007


Let me see if I understand it correctly: he used the techno track as a carrier wave, and superimposed correlations in the left and right channels (fed into the X-Y inputs on the scope) to get the nifty patterns? Or did I miss something?

In any case, it's a pretty cool (and wonderfully nerdy) use of an oscilloscope.
posted by Johnny Assay at 1:09 PM on August 30, 2007


oneirodynia, that looks like a cool project, but I was hoping for something that involved a little less risk of spontaneous and horrific death. Of course just about any project involving a CRT involves risk of spontaneous and horrific death, so I may just be out of luck. Good link though, thanks.
posted by lekvar at 1:10 PM on August 30, 2007


neustle: not quite. Looks to me like they're just driving the 'scope in XY mode. Essentially they've written a vector graphics renderer and, I would guess, are using the Left & Right channels of a soundcard as a DAC. Neat, but nothing wildly clever.

Now, if the driving signals sounded good as well, then I'd be properly impressed...
posted by Luddite at 1:11 PM on August 30, 2007


The link is not a music visualization. They've written code to more or less encode a computer display into the audio stream that the scope draws.

So they are using the scope as a monitor and programing to make it display visualizations tied to an audio stream rather than using a monitor as a monitor and programing to make it display visualizations tied to an audio stream? I'm just trying to understand why this is cool. I'm an idiot, so you might have to explain it to me as such.
posted by Pollomacho at 1:12 PM on August 30, 2007


The music that's playing in the youtube video is unrelated to the display on the scope. There is a waveform that's driving the scope, but it's not what you hear. What you hear is just a nice soundtrack for the demo.

Scopes usually have an X-Y mode, in which a pair of input signals control the X- and Y-positions of the beam. But remember, these are analog signals (voltages). He is using a soundcard as a digital-to-analog converter (which is, of course, what a soundcard is, at its heart).

The WAV file that drives the display (not what you hear) is probably stereo, with one channel controlling the X and the other controlling the Y.
posted by iconjack at 1:18 PM on August 30, 2007


Now, if you want a challenging hack, try showing video on an oscilloscope (that doesn't have a "Picture" button, obviously.)

For example: http://www.intio.or.jp/jf10zl/tv.htm
posted by Luddite at 1:19 PM on August 30, 2007


It's not that hard to show video on a scope, providing you've got a TV to hand. Depends on how much you want to cheat.

Meanwhile, here's how to turn your old TV or monitor into a lissajous display. It's surprisingly easy.

http://www.fly.net/~rupertg/onomatograph.htm

But what I want to know about the dem in the OP (which I haven't yet hooked up to my scope - I'll do so in a bit), is how they do the Z modulation.
posted by Devonian at 1:31 PM on August 30, 2007




I just wished he had used the actual waveform as the soundtrack for the video, instead of cheesy techno. I'm having a hard time syncing up playing the waveform in itunes, and the muted video in youtube.
posted by bobot at 1:41 PM on August 30, 2007


oscilloscopes are so fun to mess around with, you can make some beautiful shapes. I'm not getting my kids a TV, just an oscilloscope for the living room.
posted by milestogo at 1:54 PM on August 30, 2007


I'm not clear at all on whether the visualizations are being generated by the same audio as is audible on the track, simultaneously.

It's obviously not. I thought it would be at first, but it's not.

That said, it's pretty awesome.
posted by delmoi at 2:08 PM on August 30, 2007


The actual waveform hurts my head.
I don't think they did any Z modulation (intensity).
And I have no idea on the text, cubes and effects- I'm pretty sure you can't do that with lissajous.
posted by MtDewd at 2:21 PM on August 30, 2007


And I thought I was cool building Naughts and Crosses for the waveform monitor into my video colour bars. Oh well.
posted by sycophant at 2:43 PM on August 30, 2007


the seemed to swap between two different display modes. at times it seemed to be drawing directly with x/y inputs (when the lines were smooth). but at other times they seemed to be "faking" a pixel based display, perhaps by using the timebase on x and then controlling z.

anyway, very neat.
posted by andrew cooke at 2:56 PM on August 30, 2007


Junior EE project was to turn a scope into a monochrome TV. (No tuner, we used baseband NTSC signals out of a test signal generator or a DVD/VCR.)

Simple, really. Ramp generators (linearly increasing voltages) drive the scope X and Y, with some circuitry to reset them when you get the sync signals. At the same time amplify/shift the NTSC signal as desired and feed it to the Z (brightness) input on the scope. Actually, just the video part wasn't considered enough work, so we had to build an audio amp as well.
posted by TheOnlyCoolTim at 3:33 PM on August 30, 2007


I am a little surprised they could pull that off with only stereo audio bandwidth.
posted by exogenous at 4:05 PM on August 30, 2007


good point (bandwidth).

maybe that's why the scanned stuff is so noisy? maybe they're not scanning like a TV (ie full raster scan) but instead use just a few separate scans, each with a dedicated y control?
posted by andrew cooke at 4:10 PM on August 30, 2007


or perhaps it's not real time?
posted by andrew cooke at 4:11 PM on August 30, 2007


I notice they give the wavefrom as a FLAC file. It would be interesting to see what it looks like with various bitrates of MP3.
posted by smackfu at 5:26 PM on August 30, 2007 [1 favorite]


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