On a related note, a friend created some frequency-domain visualizations of interesting sounds using the Welch power spectral density estimation algorithm and Fast Fourier Transform, the same algorithm described in this blog post.

A few examples:

1. Dialtone using dual-tone multi-frequency signaling and 56K dial-up modem connection: https://www.youtube.com/watch?v=FomWraKuDFg&list=PLn67ccdhCs...

2. Deluxe Multitone Car Alarm: https://www.youtube.com/watch?v=A4uKcvZL7HM&list=PLn67ccdhCs...

3. Composition using only sounds from Windows 98 and XP https://www.youtube.com/watch?v=6lT-jr9sS6Y&list=PLn67ccdhCs...

4. Piano Music (Ballade Pour Adeline): https://www.youtube.com/watch?v=RnAfrEk429w&list=PLn67ccdhCs...

5. Electronic Music Demo: https://www.youtube.com/watch?v=MllJLIX1glg&list=PLn67ccdhCs...