![]() ![]() The basilar membrane is set in vibration by the sound impulses transmitted by the ossicles. The basilar membrane actually forms the lining of a snail-like structure called the cochlea. The actual receptors which are in the form of hair-like structures, also known as organs of corti varying in length are located along the basilar membrane. This membrane is known as the basilar membrane. The three bones conduct the disturbances caused by the stimulations to another membrane in the inner part of the ear. Their technical names are the incus, malleus and stapes. They are popularly known as the hammer, the anvil and the stirrup because of their shapes. These motions of the eardrum or tympanic membrane as it is called are further transmitted through a chain of three bones in the middle part of the ear. The sound waves activise the eardrum in the human ear. The functioning of the system in brief is as follows. The auditory system or the system of hearing consists of the receptors in the human ear, the auditory nerve and the temporal lobe of the cerebral cortex. This phenomenon of adaptation, it is a general characteristic of all sensory experiences, though there may be exceptions. If we continue to listen to a sound for some time, it appears to become less and less loud though the stimulus characteristic remains the same. ![]() Auditory Adaptation :Īnother phenomenon which one notices in relation to sound sensation is that of adaptation. Usually tones or sounds with lower frequency are likely to mask those with higher frequency. This phenomenon in which one tone or sound covers the other is called masking. We have all experienced that when two-tones or sounds occur at the same time one drowns or silences the other. This type of combination is an important element in orchestral music. Similarly, it is also possible to produce a summation tone where the two tones add up to produce a combined effect. The loudness of this sound is equal to the difference between the two sounds. We are all familiar with the beating of a drum. When two sounds of different frequencies are combined in quick succession, we hear a beat. Some of the experiences arising out of a combination or mixing of sound experiences are as follows: Similarly, different auditory experiences also combine and mix together. While talking about visual sensations, it was pointed out that different kinds of light rays can be mixed to give different colours. Noises have mixed frequencies and are highly heterogenous. What differentiates a noise from the sound is the high degree of irregularity characterizing the former. These overtones determine the quality of a sound sensation. Out of these patterns emerge what are known as overtones. The timbre of a tone or a sound is determined by its pattern. differentiating between different kinds of voice qualities. Similarly, we talk of rough voice, smooth voice, harsh voice etc. Thus, the sound of a violin is different from the sound of a flute. The timbre of a sound is the typical, qualitative characteristic of a sound. Thus, pitch as well as frequency is determined by amplitude. It should also be pointed out that to some extent the pressure or amplitude also influences the pitch. This intensity is measured in terms of decibels. The range of amplitudes or the amount of pressure that can operate on the human ear is very wide. The amplitude of soun4 waves determines the pressure on the human ears and this, in turn, determines the loudness of the sound. The loudness of a sound depends on the amplitude of sound waves. As the frequency increases the pitch gets higher and higher. Sounds are categorized as low pitched and high’ pitched. ![]() The pitch of a sound is dependent on the frequency of the sound waves. ![]() These dimensions or characteristics of the sound sensations correspond to different characteristics of the sound stimuli which impinge on the human ears and the receptors therein. We can, therefore, see that the different sounds we experience differ in many dimensions. Some sounds are pure while other sounds are mixed, thus, showing different degrees of timbre or quality. Some sounds are loud and others not so loud. Some sounds are heard for a short time and some for a long time, some have a high pitch being very shrill like a scream while others have a low pitch and are not shrill. Different sounds last for different durations. The major dimensions are duration, pitch, loudness and timbre. The various sound sensations we receive, differ in a number of dimensions. Sound waves below sixteen and above twenty two thousand are not generally heard. The human ear can respond to a wide range of sound waves ranging from sixteen decibels to nearly twenty-two thousand decibels. ![]()
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