[ssgh]

I've been casually researching visualisations of sound for 2 years now, and recently came across another interesting discovery, and wanted to share it.

It slightly improves the way ACF images are presented, but this small improvement makes a big difference. It works best on "small sounds" that last 1-2 sec, such as vowels or sample recordings of flute, violin and so on. The sound is analysed with FFT with the sliding window of 1/4 sec that advances by 1/500 sec at a time until it covers the entire waveform. After computing FFT spectrum for each frame, a basic bandpass filter is applied to separate high and low frequencies. The result is fed to the inverse FFT, thus computing ACF, and presented in polar coordinates using a basic red-blue color scheme. The effect is that low frequencies appear red and high frequencies appear blue.

To my surprise, this basic method reveals a large variety of distinctive, yet visually appealing, shapes for vowel sounds.