![]() ![]() On a logarithmic scale, however, the changes between two values are based on multiplication (or orders of magnitude). Likewise our hearing does not have the same sensitivity at all frequencies. On a linear scale the change between two values is based on the difference between them for example, moving from 20 to 30 on a linear scale represents a difference of 10. ![]() No microphone has the same sensitivity to all frequencies and no speaker reproduces all frequencies equally well, as we will see in Chapter 18 on electronics. The decibel scale The ear mechanism is able to respond to both very small and very large pressure waves by virtue of being nonlinear that is, it responds much more efficiently to sounds of very small amplitude than to sounds of very large amplitude. The above curves are very much like the frequency response curves of microphones and speakers. This function converts a decibel value into the linear ratio between two voltages or powers. ![]() To help us understand the difference, let’s take a look at linear growth on a graph. Medium loudness doesn't change the perceived pitch very much. The decibel employs a logarithmic scale, not a linear one. Low frequencies are perceived to be slightly lower than expected if they are very loud. High frequencies are perceived to be a slightly higher pitch than normal if they are very loud. It is also the case that intensity has an effect on perceived frequency the same laboratory frequency will appear to be a slightly different frequency if the intensity is different. \( \newcommand\) is due to the tube resonance of the auditory canal (see chapter 12 for tube resonance and chapter 10 for a picture of the auditory canal). ![]()
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