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How to convert two audio channels into X-Y composite video ?

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Jan 29, 2004
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Hello all.
Stereo audio can be fed to an oscilloscope in X-Y mode to display lissajous images on its screen.
How to convert such 2 audio signals as composite video to feed that input of a plain modern LCD television to show the lissajous waveforms ? Is there such gadget already on the market ?

Indeed Youtube has videos of oscilloscopes displaying images very much like tv pictures. You could say they're lissajous figures. The XY signals are generated by a programmable device.

Do you mean stereo audio signals? Then feed one channel to the horizontal input, and the other channel to the vertical input.
Identical content creates a diagonal line.
Stereo content creates a cloud of traces which is roughly diagonal.

Or to test an amplifier for distortion, feed your initial signal to the vertical input, and the amplified signal to the horizontal input.

My oscilloscope (vintage Tektronix tube-type) requires a few volts amplitude in the horizontal signal, in order to make the beam travel the entire width of the screen. The vertical signal can be just a few mV.


Reading your question again I realize you're interested in turning an lcd television into an oscilloscope, rather than vice-versa as my surface thinking led me.

There are computer programs which utilize the internal sound card, accepting audio through the mic input of a computer, and painting pixels at appropriate heights on the screen as it reads sound card values.
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Thank you.
Yes, stereo audio each channel into H, V deflection. As LCD televisions do not have the H, V deflection coils to fed the audio into, would like to know if the stereo signals can be processed and fed as composite video into that plain LCD television input by some signal manipulation, to obtain the Lissajous images. Monochrome is fine. If an existing gadget on market does it, fine.
If I understand your suggestion; I would need a stereo sound card in a computer to display the two channel, a program to do the differential X-Y signals and if the Lissajous output is in VGA form, convert them to composite.

I would need a stereo sound card in a computer to display the two channel, a program to do the differential X-Y signals and if the Lissajous output is in VGA form, convert them to composite.
Yes, or any similar solution that acquires the analog X/Y waveforms to a digital processor, forms a bitmap graphic in memory representing the Lissajous figures and scans it to generate video output. Any modern digital oscilloscope is essentially doing the same.

I was very impressed with a quadraphonic sound display in our early 70s Engineering relaxation room. with 6?x 4" long coil speakers in each box top mounted with a tilt.

Equally impressive was a CRT TV based quadraphonic audio display, which rectified three channel equalizer Peak amplitude into one of the three primary colours but ports summed as a 2*2+\-vector with a rotated yolk by 45° then displayed the beam pattern of four channel audio from the center. This provided a very dynamic representationof what we heard.
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