Animal Ears A plain-English guide to hearing
The handful of words that come up around here, explained without the jargon.
- Audiogram
- An animal's hearing report card: a graph showing the quietest volume it needs before it starts to hear each pitch. The lower the line sits, the sharper its hearing. It's the same kind of test they run on you at the audiologist.
- Ultrasound
- Sounds so high your ears no longer register them: above about 20,000 Hz. To you they are total silence, but a dog, a cat or a bat hears them perfectly. That's exactly where a ‘silent' dog whistle lives.
- Infrasound
- Sounds so deep your ears no longer register them: below about 20 Hz. Rather than hearing them, you'd feel a tremor in your chest, like a heavy lorry going past. Elephants and pigeons do sense them, even from miles away.
- Hertz (Hz)
- Hertz count how many times per second a sound vibrates. Few vibrations = low (the rumble of thunder, about 30 Hz). Many vibrations = high (a microwave beeping, about 3,000 Hz). And ‘1 kHz' is just shorthand for 1,000 Hz. You hear, roughly, from 20 Hz to 20,000 Hz.
- Hearing threshold
- The quietest volume at which a sound stops being silence: the exact point where an animal starts to hear it. The lower that point, the finer its hearing.
- Particle motion
- Your eardrum catches the pressure of a sound, like a sail catching wind. Plenty of fish and invertebrates do something else: they feel the tiny back-and-forth of the water or air as the wave passes. It's closer to feeling sound than hearing it.
- Equalisation
- Turning the lows, mids and highs up or down separately. It's what the bass and treble knobs on a stereo do, and it's exactly what Animal Ears does to your sound to leave it the way each species hears it.