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Thread: Analog abstract generators?

  1. #1
    Join Date
    Dec 2007
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    Default Analog abstract generators?

    Hi,

    Does anybody here have technical insights into analog abstract pattern generators?
    I have a lot of analog modular synthesizers so I have most of the modules for generating complex patterns and the signal levels is almost the same between ILDA and most analog synthesizers so I want to integrate the lasershow into my music if possible.

    I'm curious if the old generators or scanner amps included some protection circuits?
    The maximum acceptable input frequencies are guite low (in jusical standards anyway)for ordinary laser galvanometers and some of my synthesizers can go as high as 100kHz.
    I'm thinking of having very steep adjustable lowpass filters set to something like 3-4khz as as start.
    I know that the scan angle is important in deciding the maximum input frequency, another variable to count in to it...
    Protecting the scanners from excessive amplitude is easy, synthesizers can be unpredictable at times so I have already included that in my planning for the "synth to laser" interface.

    I have some cheap 12k and 30k galvo sets from laserphoto.com that is going to be my test subjects.

    Any thoughts?

  2. #2
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    Default

    dar303;

    I believe 3-4 Khz is going to be too high for your low-pass filter. According to Bill Benner, the maximum small signal bandwidth on a set of 30K scanners is roughly 2.5 Khz. (Here's a great thread that talks about the derivation of that number... The meat of the discussion starts at around post # 33 or so.) And remember that even at 2.5 Khz you've got significant distortion. (The center circle on the ILDA test pattern is actually a 12-sided polygon, but it scans as a circle. That's a pretty significant margin of error.)

    Still, your project sounds very interesting. Please keep us posted on your progress. (And remember that we like pictures! )

    Adam

  3. #3
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    Check out a program called GoldWave.

    http://www.goldwave.com/

    You can create an empty stereo wave and then use the expression evaluator to populate the wave with all sorts of sin, cos, abs, etc...

    When I first started playing with lasers, I used this to make all kinds of laser doodles.

    You can also use it to write filters that take wave data as input.

    There is a nice section on the expression evaluator in the help. It is worth printing on paper!

    Also note: If you stick with true periodic functions, you'll always have the same amount of displacment above and below the zero volt line. Which means that you do not need to modify the sound cards to recouple the DC output from the DAC.

    James.
    Last edited by James Lehman; 05-27-2008 at 11:21.

  4. #4
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    Thanks for the tip, but i'm actually going to do this in analog hardware (no computer) , I have ringmodulators, sin/cos voltage controlled oscillators, delays, voltage controlled amplifiers etc.

  5. #5
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    Default

    You can get neat and predictable results if you use sine wave generators at fairly low frequencies.

    Just by setting the X axis to a 100Hz sine and the Y to something close, but tunable will make pictures that look like Spiro Graph.

    As long as you use sine (not square, pulse, triangle or sawtooth) you will have no harmonics (except for distortion). You don't really need to put a low-pass filter on a mathematically mixed set of sine waves. You should be able to tell what the highest frequency component of the resulting wave is. You can test a lot of your ideas on an O-scope.

    You can add sines of different frequencies together, amplitude modulate one sine onto another, etc. As long as the signals going to X and Y are different, you'll get some kind of crazy pattern.

    For best results, keep in mind that the higher the sine wave frequency, the less overall effect it should have in the resulting mixture.

    You can emulate all of this in GoldWave too!

    James.

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