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Frequency 0 <br /> Frequency is the time rate of repetition of a periodic phenomenon . <br /> The traditional unit for frequency in the United States was at one time <br /> "cycles per second ." Now, we use "Hertz ," abbreviated "Hz ." Only the <br /> name has changed; the meaning hasn ' t . <br /> To represent the total noise of any source , acousticians break the <br /> 1 <br /> noise into frequency components . In other words , tiow much is <br /> low-frequency noise , how much is middle-frequency noise ) how much is <br /> high-frequency noise? This breakdown is essential to any comprehensive <br /> study of a noise problem for two reasons : <br /> ▪ People react differently to low-frequency and high-frequency <br /> noise , because high-frequency noise is much more disturbing. It <br /> is also more capable of producing hearing lossl. <br /> . Engineering solutions to a noise problem are different for <br /> different frequencies . (Low-frequency noise is generally harder <br /> to control . ) <br /> The frequency distribution of a noise is determined by passing the <br /> noise successively through several different filters that eparate the <br /> noise into 8 or 9 octaves on a given frequency scale . Just like an <br /> octave on the piano keyboard of Fig. 3 , an octave in sound analysis <br /> represents the frequency interval between a given frequencylr, such as 300 <br /> Hz , and twice that frequency , which for 300 Hz would be 600 Hz. <br /> 2 OCTAVES <br /> ABOVE <br /> MIDDLE C MIDDLE C <br /> luleil 111111 <br /> 261.6 Hz 1046 4 Hz <br /> L <br /> 125 250 500 1000 2000 4000 <br /> OCTAVE BAND CENTER FREQUENCY (Hz) <br /> FIG. 3. PIANO KEYBOARD OCTAVE. <br /> 10 <br /> 01.tftyrr Sfrrr:$ st' " • • <br />