Decibels are important in microphones, both in terms of the acoustics and the electronics. Key microphone parameters such as signal-to-noise ratio, sensitivity, and frequency response are specified in decibels (dB). In general, decibels are used when measuring things that have very large ratios, a good example of that is human hearing. Consider the softest sound that can be heard, maybe a whisper or a person breathing, and then compare it to the output of a jet engine; humans can hear an incredibly wide range of sounds. Decibels are a convenient way to represent that range. A convenient feature with decibels is that instead of multiplying and dividing, they use addition and subtraction. For example, adding 3dB to a signal is the equivalent of multiplying the signal by two, or subtracting 3dB is the equivalent of dividing by two. Likewise, adding or subtracting 10dB is the equivalent of multiplying or dividing by a factor of 10; 20dB would be the equivalent of multiplying or dividing by a factor of 100. Working in decibels makes life easier. There are different types of decibels that are used when discussing microphones. The output of digital microphones is given in dB FS, where FS stands for full scale. In this case, the dB is measuring the ratio between the microphone output at a particular signal level and its full scale output, hence dB FS. The term dBV is used when discussing analog microphones, it is a measure of the microphone’s output in comparison with a standard of one volt. The third type of decibels used with microphones is dB SPL, which is used for measuring the sound pressure level, the input to the microphone.