Useful approximations

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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.


  • 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)


  • 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.
  • A quarter of a decibel change in intensity is the threshold of perception.

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 between samples