Being able to hear means hearing many thousands of different sounds and tones. People do not just hear a sound. We perceive a combination of frequencies (pitches) and the sound pressure level of these tones.
Frequency, measured in Hertz (Hz), is an indication of the number of vibrations per second that are received by our ears. Subsequently, the middle ear, the internal ear and the auditory nerve transfer these to the brain for processing. On average, people perceive frequencies between 20 and 20,000 Hertz. The range between 500 and 4000 Hertz is felt as being pleasant. For instance, human language and music are within this range (of course, dependent on the sound volume).
Sound pressure level, measured in decibels (dB), indicates the pressure with which the sound waves reach the eardrum. The higher the value, the louder the tone. The lower threshold is 0 dB – the bottom limit of what is audible. If something sounds softer than 0 dB, it is impossible for a human being to perceive. The level of a normal conversation is about 50 dB. Noise becomes painful at about 120 dB.
Pure tones, such as the well-known concert pitch A, always vibrate with a certain frequency.
Sounds are a combination of various tones. Also vowels, being a–e–i–o–u, are sounds.
A sound is formed by various frequencies acting in a cluster. They create, for instance, hissing, whistling or buzzing sounds. This implies that all consonants in our language are sounds as well. Also ambient noises, such as traffic, flowing water or the waves of the sea, are examples of this. The higher the tone, the sharper the sound. For example, the song of a bird can consist of high tones. An example of low tones is far-away thunder or the sound of a bass guitar.
Being able to hear is:
understand a conversation. Communication with others is contact with people.
hear warning and signal sounds. The siren of an ambulance, the beep of the microwave, the doorbell and the rattling sound of a traffic light are sounds that make us feel safe.
recognise sounds. A dripping tap, a pan boiling over, a breaking glass: all these give us important information about what action we have to take. Also think of the intonation of someone’s voice by which we know that someone is making a joke or hearing someone’s voice breaking.
hear direction. As the eyesight deteriorates, being able to hear where a sound is coming from becomes all the more important. Especially outside when participating in traffic this increases our sense of security.
hear distance. People who are hard of hearing and whose eyesight is deteriorating, can sometimes be given a fright when suddenly someone is standing beside them. Because of the high level of sound processing in the modern hearing aids, this aspect of hearing is often forgotten.
hear calming sounds. Being able to hear the sounds in nature, such as the songs of the birds, the murmur of the sea and water running in a stream, can bring relaxation and rest. People suffering from Usher Syndrome have a higher risk of over-stimulation and over-tiredness. Being able to hear these comforting sounds of nature enhance recovery and rest.
experience music. Listening to music is a relaxing way of hearing but not listening with much effort. Music touches our emotions and has an effect on our moods. Some people argue that often listening to music helps to better understand speech. Music teaches us to distinguish a lot of sounds in all pitches and intensities. Here it doesn’t matter whether we listen to classical music or to rock, blues or jazz.
The intensity of sounds, also called ‘loudness’, is measured in decibels. Therefore the level of loss of hearing is also determined in decibels (dB).
The figures given below give an impression of the volumes of certain sounds:
- whispering ± 30 dB,
- normal speech ± 60 dB,
- shouting ± 80 dB,
- lorry ± 90 dB,
- drilling machine ± 110 dB.