What do we hear?

We humans don’t just hear sounds but rather a combination between frequencies and the sound pressure level of these. The following terms are important to know when we talk about hearing:

Frequency, measured in Hertz (Hz), indicates the pitch of the sound. Sound travels in waves, and the higher the number of waves a sound has per second, the higher the pitch. Once a sound wave reaches the ear, it is processed by the various parts of the hearing system. On average, humans are capable of hearing sound frequencies ranging from 20 to 20,000 Hertz. The frequencies between 500 and 4000 Hertz are particularly pleasing: this is the range of most human speech and music.

Sound pressure level, measured in deciBels (dB SPL), indicates the pressure of the sound waves that hit our ears. The higher the pressure, the louder the sound. Our auditory threshold, the limit of what we can hear, is 0 dB SPL. A normal conversation is about 50-60 dB SPL. The pain threshold is found at about 120 dB – this is where our hearing can be instantaneously damaged and deafness can occur.

Pure tones are sounds that are made up of only one frequency, instead of a combination.

Complex tones are the opposite of pure tones. They are sounds made up of several frequencies at the same time, for example the English vowel sounds of a, e, i, o and u.
what can't humans hear?

What can't we hear?

Our range of hearing is from 20 to 20,000 Hertz and so wide that we can tell the difference between about 400,000 different frequencies. Of course, there are many more frequencies that even people with perfect hearing simply cannot hear, because they fall outside our hearing range. For instance, the human ear cannot process ultrasonic sound waves.

In New Zealand, 6 out of 10 over 60, and 1 in 6.of all Kiwis suffer from hearing loss, with many of these experiencing age-related hearing loss.
Age-related hearing loss is caused by changes in the sensory part of the inner ear. Over time, people with age-related hearing loss will find it harder, particularly, to hear high frequency sounds. This affects how clearly they hear and understand speech, as well as making it more difficult to understand sounds in noisy environments.
If you notice that you have trouble understanding people around you, make an appointment with a Triton Hearing clinician. With a 20-minute hearing health check, you will know how well you are able to hear, and what sounds you may be missing.

What do others hear?

There are many frequencies that cannot be perceived by human ears. Our ears cannot hear particularly deep tones in the infra-sound range as well as particularly high-frequency tones of the ultra-sound range – however, some animals can. Elephants, cattle and insects can hear very deep sounds below 16 Hz whose sound waves spread across vast distances. Hedgehogs, bats and – the undisputed champions – dolphins (which can hear pitches above 100,000 Hz) are found at the other end of the spectrum. Their hearing systems perceive other ranges of frequencies, meaning they have a different hearing threshold from us. The voices of these animals also differ in conjunction with their range of hearing and only partially overlaps with the human range of hearing and voice field. Animal communication is thus partially outside of our perception.

Dolphins also ‘see’ with their ears: they use the echo of their clicks – their high-frequency sound pulses – to identify the location of potential predators and prey. This allows them to acoustically locate and hunt even small fish. By the way: dolphins also produce individual whistling sounds that serve as sort of acoustic fingerprint.