A comparison of logarithmic vs. linear scales.
These two MP3 files each play ten tones, increasing from 200 Hz to 2000 Hz.
"rising-linear.mp3" increases the frequency by 200 Hz each step. The frequencies are thus 200 Hz, 400 Hz, 600 Hz, ..., 2000 Hz. But to the human ear, it sounds like it increases quickly, but then levels out.
"rising-logarithmic.mp3" multiplies the frequency at each step by the 9th root of 10 (~1.29). Thus the frequencies are roughly 200 Hz, 258.3 Hz, 333.6 Hz, 430.9 Hz, 556.5 Hz, 718.8 Hz, 928.3 Hz, 1199.0 Hz, 1548.6, and 2000 Hz. These pitch changes sound much more level to the human ear, even though in absolute terms the frequency changes start small and end much larger.