This phenomenon is seen with many music instruments. Therefore it can be expected that the relative amount of overtones at the lowest frequencies strongly increases. However, the decreasing sensitivity of the ear indicates that the membrane is relatively вЂњstiffвЂќ for this frequency range.

To my knowledge, nobody has ever investigated the frequency spectrum of the basillary membrane at very low frequencies. Nonetheless, we only hear a pure sine-wave at the fundamental frequency since our brain has learned that this specific frequency spectrum belongs to a pure tone. Harmonic distortion in the inner-ear thus sums up to approximately 60%! For sine waves between 2 Hz these overtones have amplitudes of 33%, 13%, 6%, 4%, 2%, вЂ¦. Mechanical harmonic distortion in the inner ear:ДЄ pure 200 Hz sine wave not only makes the basillary membrane inside the ear vibrate at 200 Hz, but also at 400, 600, 800, 1000, 1200вЂ¦.

However, the вЂњcolorвЂќ of the note is lighter when the fundamental tone is missing. Since the 6 Hz frequency components are no fundamentals of the lowest (400 Hz) frequency component present, our brain knows that something is missing and вЂњaddsвЂќ an imaginary fundamental tone of 200 Hz. Nonetheless our brain tells us that the pitch of the note is 200 Hz. If we electronically remove the 200 Hz fundamental tone our ear only hears the harmonic frequencies at 400 Hz and higher. The sound of a single note of a music instrument is the summation of its fundamental tone (say 200 Hz) and a number of harmonics (400, 600, 800, 1000, вЂ¦. The principle of the missing fundamental: The device combines two psychoacoustic phenomena. In this article a device is presented that makes signals below 60 Hz audible in loudspeakers and headphones that normally, by their mere physical construction, are not able to reproduce these frequencies. Another example is the loudness button on many amplifiers that compensates for the reduced sensitivity of the ear for the highest and lowest frequencies at low sound pressures. An example of psychoacoustic processing is data compression with MPEG-3, which removes information from the signal without (or almost without) affecting sound quality. Principles of psychoacoustics are widely used in audio technology. The study of the physiological and mental processes of hearing is called psychoacoustics. For instance, in well known optical experiments straight lines may look bent or equally long lines seem to have different lengths These experiments tell us, that the brain processes involved in perception also play an important role in the way we see and hear our world. Nonetheless, eyes and ears are also easily fooled. We can distinguish the slightest gradations in intensity, color, frequency, etc. Our senses, especially our eyes and ears, are remarkably precise instruments.

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