The graphic on this page, taken from a Wikipedia entry, shows the current ISO standard for something called equal loudness contours.
If you've studied audio production or audio equipment, you might have seen this or similar charts. (The earliest version, created in 1933, was known as the Fletcher-Munson curve, and recent studies have proven it was quite accurate.) But what does it mean?
The horizontal x-axis represents pitch, measured in Hertz (Hz), or vibrations per second. The lowest threshold of human hearing is around 20 Hz--that would be a very low bass note on a church organ. Human voices … Read more