X-Y waveform display

[Terry Payman]

I love waveform displays, but greatly prefer to see a fixed pattern displayed if there is a constant/sustained musical tone. This is rarely the case using Magic, as the fixed audio sample window is generally not close to a integral number of periods of the audio being displayed.

An X-Y display solves this problem when the axes are both driven by filtered versions of the audio. In effect the audio is plotted against its own harmonics, so the pattern is always static if the harmonic content is constant in phase and amplitude.

With oscilloscopes I have used a technique I adopted (decades ago) from formant analysis. A 1st-order low-pass filter drives the X-axis, 1st-order high-pass (with same crossover frequency) drives the Y-axis. Whilst searching for an on-line example I came across what is probably a more general method which avoids the need to select a crossover frequency: feed the X-axis with unfiltered audio and the Y-axis with 90-degree phase shifted audio (ie an all-pass filter). The visual result is virtually the same, so the video is a good example.

Here's the example (by John Matthew Tennant). See how the display is frequency-independent.

http://www.johnmatthewtennant.com/

A further refinement is to have intensity modulation from a third audio channel (sorry, no example yet).

Ideally Magic would have integral audio filters that could feed the waveform displays. I had to make many separately filtered audio files to give the "building-block" waveforms I used for my competition entry:

[Sadler]

Those shapes in the video are very interesting but I'd imagine they'd be more suited to 8bit music and certainly not grungy rock. I don't know what could be achieved by filtering but your vimeo video that you took your still from shows the potential.

Something similar on shadertoy is this: https://www.shadertoy.com/view/Xsf3WB

[Magic]

feed the X-axis with unfiltered audio and the Y-axis with 90-degree phase shifted audio (ie an all-pass filter). The visual result is virtually the same, so the video is a good example.

Looks very interesting! I will definitely have to do some exploring.

Something similar on shadertoy is this: https://www.shadertoy.com/view/Xsf3WB

Also pretty cool .