In a nutshell, you connect the left and right channel of your audio source to an oscilloscope while playing it through an amplifier. Set the oscilloscope to X/Y mode and the oscilloscope will draw a picture according to the instantaneous audio voltages. But the art is to create audio signals which draw a nice picture and create an equally pleasant sound.
In this demo, I am using the software from this blog post and copied some of Jerobeam’s files onto an SD card. So what you see here is the Zedboard pumping hundreds of megabytes through the DMA controller into the audio codec.
If you are into this kind of thing, you should really buy the WAV files in Jerobeam’s online shop. It is really not expensive. And it is essential to get uncompressed WAV files because artefacts caused by audio compression codecs (such as mp3) will distort the picture.
Here is how the rudimentary user interface of the software:
If you look closely, you will find that there are quite a few ghost images. I think, this is because the audio output is AC-coupled. If I have time, I might try again and bypass the output capacitors.
Here is the the post with the complete software: