Audio Fact(s) of the Day

Hi there!

I just wanted to post some random facts about sound and how we perceive it. I encourage you to follow the links and find out more. Well, here you go:

• loudness is not directly proportional to the pressure that sound wave applies to your ear;
• sounds of the same pressure but different tones would appear to have different loudness. Humans are most sensitive to frequencies from about 2 kHz to 5 kHz. A-weighting curve (along with a bunch of others) describe the connection;
• furthermore, loudness depends on the duration of the tone. Basically, it is an integral of the sound intensity (air pressure) during the previous 600–1 000 ms;
• there’s no single unit to measure loudness. We have dBSPL, decibel using 20 micropascals as a reference value. There’s dB(A), which is just dBSPL corrected in accordance with A-weighting curve. There’s also phon, defined as an equal to 1 dBSPL at a frequency of 1 kHz, and then scaled for other frequencies, forming equal-loudness contour;
• in digital systems it’s all backwards: 0 dBFS (“decibel relative to full scale”) is the loudest sound possible, and anything else is encoded by negative values (e.g., -3 dBFS is half as loud as possible);
• bands of proportional width are perceived as if they have the same width. E.g., difference between 20 Hz and 30 Hz seems to be the same as between 200 Hz and 300 Hz;
• science that studies perception of sound is called psychoacoustics;
• vuvuzela horn at 1 meter away from your ears produces 120 dB(A) sound. Threshold of pain is 130 dB;
• you need about half a minute of listening to 115 dB sound to damage your ears;
• specifics of human hearing can be described with psychoacoustic model. It is then used in “lossy” codecs (MP3, Ogg Vorbis, etc.) to exclude sounds that you are unlikely to hear, thus allowing for better compression;
• striving to make songs stand out, companies apply dynamic compression. It makes quiet sounds louder, increasing overall loudness while robbing songs of their emotional power. This phenomenon is called loudness war.

Hope you learned something new. See you!