9.4. Auditory Sensitivity Function

Like light waves, the physical properties of sound waves are associated with various aspects of our perception of sound. The frequency of a sound wave is associated with our perception of that sound’s pitch. High-frequency sound waves are perceived as high-pitched sounds, while low-frequency sound waves are perceived as low-pitched sounds. The audible range of sound frequencies is between 20 and 20000 Hz, with greatest sensitivity to those frequencies that fall in the middle of this range.

The unit of the loudness of sound is the decibel (dB). For example, an ordinary conversation is approximately equal to 60 decibels (dB), and a rock concert is approximately equal to 120 decibels (dB). These are all examples of different levels of sound loudness in daily life. The lowest of the human hearing range is approximately equal to a whisper at a distance of 5 feet (Figure 9.6). When comparing loudness across frequencies, we see (Figure 9.6) that lower frequencies and very high frequencies need to be made louder in order to appear as loud as frequencies in our most sensitive range.

We are most sensitive to sounds in the range of 1,000 – 3,000 Hz, where important information in conversational speech tends to be. Musical notes occupy a smaller range, from about 28 Hz to just over 4,000 Hz. The speech of a typical adult male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz.

Dogs can hear above 40,000 Hz; dolphins can hear up to 150,000 Hz. Additionally, chickens have a very limited audible range, from 125 to 2000 Hz. Mice have an audible range from 1000 to 91000 Hz, and the beluga whale’s audible range is from 1000 to 123000 Hz. Our pet dogs and cats have audible ranges of about 70–45000 Hz and 45–64000 Hz, respectively (Strain, 2004). See Figure 9.7 to compare frequency ranges across animals.