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useful_approximations

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.
  • A quarter of a decibel change in intensity is the threshold of perception.
  • 30 dB SPL is basically unattainably quiet, 60 dB SPL is a normal conversion, 90 dB is around where hearing damage begins
  • An increase of 9 dB corresponds to roughly a doubling in perceived loudness.

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

Instruments

  • Guitar frequency range: 82 Hz to 1,300 Hz (E2 = 82.34, 4 octave range)
  • Electric guitar pickup output varies from .1 to 1 V RMS, depending on pickup strength
  • Piano frequency range: 28 Hz to 4200 Hz (A0 = 27.5, 7+ octave range)
useful_approximations.txt · Last modified: 2015/12/17 21:59 (external edit)