What do we hear?
We humans don’t just hear sounds but rather a combination between frequencies – meaning tone pitches – and the sound pressure level of these tones. The following terms are important to know when we talk about hearing:
Frequency, measured in Hertz (Hz), indicates the oscillations per second that hit our ears. There, they are further processed by the various stations of the human hearing system. On average, humans are capable of hearing frequencies ranging from 20 to 20,000 Hertz. Particularly pleasing is the range from 500 to 4,000 Hertz. This is the range of human speech and music (depending on the volume, of course).
Sound pressure level, measured in decibels (dB), 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. Human beings simply cannot hear anything quieter than 0 dB. A normal conversation measures about 50 dB. The pain threshold is found at about 120 dB – this is where our hearing can be damaged and deafness can occur.
Pure tones – such as the famous concert pitch A – always oscillate with a certain frequency.
Complex tones always consist of several tones. Auch Vokale, also a - e - i - o - u, sind Klänge.
A sound is created from many bundled different frequencies. This results in a hissing, whistling or humming. The consonants of our languages are thus sounds. This also includes environmental sounds like traffic noises or the swoosh of the water at the sea.
What are we incapable of hearing?
Our range of hearing is from 20 to 20,000 Hertz and so wide that we can differentiate between about 400,000 different tones. Of course, there are many more frequencies that even people with perfect hearing simply cannot hear, because they fall below our hearing threshold. For instance, the human ear cannot process ultra-sound waves. Such tones literally remain unheard.
The majority of deaf people suffer from age related deafness, but even some young people can be affected by impaired hearing.
Age related deafness is caused by the small hair cells in the inner ear dying off which most often results in patients no longer being able to hear particularly high frequencies in the beginning. Without being fitted a hearing aid in time, hearing is further impaired until the human brain looses the ability to correctly attribute tones.
If you notice that you have trouble understanding your counterpart, make an appointment with a Connect Hearing acoustician or your doctor. In a matter of 15 minutes (the average time a hearing test takes) you will be sure and know how good your hearing is.
What do others hear?
Beyond our ears, there are many tones and sounds that cannot be perceived by humans. Our ears fail to hear particularly deep tones in the infra-sound range as well as particularly high-frequency tones of the ultra-sound range – some animals can, however. 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. They all 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, so to say. They use the echo of their clicks – their high-frequency sound pulses – to localize the bodies of potential predators and prey. This enables them to acoustically locate and hunt even small fish. By the way: Dolphins also produce individual whistling sounds that serve as as sort of acoustic fingerprint.