Hearing Practics

Hearing — The Ear

  • Physics of hearing

  • Note that the ear detects frequency directly

  • The measured sound amplitude is logarithmic in the sampled sound power: big differences at low power, small differences at high power

  • Thus usually use units of dB instead of linear power

    P[dB] = 20 log (P[rms] / 10^-12)
    
  • C.f. "type A" and "type B" potentiometers as "volume knobs"

Hearing — Psychoacoustics

  • The brain does things with sound…

  • Perceived volume of a sound is a function of

    • Background volume level: individual sounds seem less loud in a noisy environment

    • Waveshape: in particular, the brain will "fill in" "clipped" waves as though the peaks exist. This is used by broadcasters to make sounds seem louder than their measured power

  • Perceived frequency of a sound is

    • Relative: "perfect pitch" is rare; pitch is mostly judged by relation to surrounding / background / earlier pitches

    • Dominated by high frequency components: dbA frequency weighting is used as an estimate of perceived loudness

  • Accomodation over time, etc happens

  • Shepard Tone is an interesting audio illusion

Hearing — Safety

  • Easy to damage hearing permanently

    • Sound exposure is cumulative: long exposure to a moderately loud sound is more damaging than short exposure to a somewhat louder sound

    • NIOSH: More than 85 dBA (heavy city traffic) over 8 hours is hazardous

    • Acute trauma over 130 dBA

    • Not just general hearing loss: notching, tinnitus

  • How to stay safe:

    • Wear ear protection around sustained loud noise: concerts, machine rooms, etc. Wear noise-cancelling headphones on airplanes

    • Avoid earbuds, as they are prone to hearing damage. If you use them, turn them down to below where they sound best: the ear / brain don't know how to deal with them

    • Turn down master volume before powering up any audio equipment. Then raise the volume to a comfortable level

    • Put headphones on your neck to start; you should hear silence. Then put them on and turn up the volume

    • See above when working with mute buttons, plugs and jacks, etc. So easy to make a mistake

Hearing — Two Ears

  • Normally hear in stereo; thus two-channel audio with separated sources (headphones, left and right speakers)

  • Means two audio channels to deal with: stereo is sometimes encoded as sum and difference channels, with the difference channel at lower fidelity

  • Localization in space is a function of time difference and level difference between ears

    • Angle:

      • Phase is used below 1KHz

      • Head interference and group delay is used above 1.5KHz

      • This is part of what the "ears" (pinna) do

    • Distance:

      • Softer, lower-frequency sounds seem farther away

      • Room effects (reflection) increase perceived distance

Last modified: Monday, 30 March 2020, 11:23 AM