Useful approximations

This is an attempt to keep track of the various numbers and approximations that are good to have in your hip-pocket when studying audio and music.

Physics

• Sound travels roughly 1 foot every millisecond.
• Typical t60 for a small, house-sized room is .5 seconds, for a larger room (eg, classroom) it's about 1 second.
• A 20 Hz signal has a period of 50 milliseconds ( .05 seconds), a 20,000 Hz signal has a period of 50 microseconds ( .00005 seconds)

Perception

• Humans can usually hear from about 20 Hz to 20,000 Hz (20 kHz)
• Perception of "loudness" for different frequencies is (very) roughly flat from about 100 Hz to 10 kHz, for most decibel levels. Pitches sound much less loud outside of this range.

Digital Audio

• About 6 dB of Signal to Noise Ratio is gained per bit when quantizing continuous values.
• In order to avoid aliasing, the sampling frequency must be two times that of the highest frequency present in the signal.
• 44100 Hz = .00002675737 seconds between samples, 48000 Hz = .000020833333 seconds per sample