Frequency is a term used to describe tone and it is measured in Hertz . Low tones are known as bass, midrange tones are in the range of the human voice, and high tones are musical instruments such as a cymbal. The human ear is capable of hearing low tones from approximately 20 Hertz (abbreviated 20Hz) to high tones up to 20 kilohertz (abbreviated 20kHz). 20 Hz is very low, deep bass and 20kHz is probably beyond the range of human hearing. The range of human hearing is dependent on the health of the ear and age. As we age, our range of hearing is reduced.
Frequency response is the term used to describe the range of tones that a stereo system can reproduce. Typically a system is capable of frequency response that ranges from 20Hz to 20kHz, the approximate range of human hearing, and most people would consider this to be adequate. Many times, however, manufacturers will report specifications that claim frequency response that extends to 100kHz, five times greater than the highest range of human hearing. If you can’t hear it, why reproduce it? Well, there is some logic to their claim.
Musical instruments produce a wide range of frequencies called fundamental frequencies and harmonic frequencies. For example, a middle C played on a piano has a frequency of 440Hz, called a fundamental frequency. The fundamental frequency also has harmonics, which are multiples of the fundamental. The first harmonic of 440Hz is 880Hz, twice the frequency of the fundamental. The second harmonic is 1320Hz; the third is 1760 and so on. A musical instrument produces a characteristic sound because of the combination of the fundamental and harmonic frequencies. A piano playing a middle C note sounds different that a violin playing the same note because of the harmonics of each instrument. Some audio scientists believe that the complex human ear-brain system is capable of perceiving the fundamental frequency and the harmonic frequencies even well beyond the range of human hearing and these out-of-range harmonics influence our perception of reproduced music. So, even if you can’t ‘hear’ 40kHz, or 60kHz, your senses are capable of perceiving them and they influence your judgment about musicality. Makes sense to me.