Click here to purchase the entire book in PDF format. Gain Lesson 1 for almost all recording engineers comes from the classic movie ``Spinal Tap'' where we all learned that the only reason for buying any piece of audio gear is to make things louder (``It goes all the way up to 11...'') The amount by which a device makes a signal louder or quieter is called the gain of the device. If the output of the device is two times the amplitude of the input, then we say that the device has a gain of 2. This can be easily calculated using Equation 2.13. $$\textrm{gain} = \frac{\textrm{amplitude out}}{\textrm{amplitude in}}$$ (3.13) Note that you can use gain for evil as well as good - you can have a gain of less than 1 (but more than 0) which means that the output is quieter than the input. If the gain equals 1, then the output is identical to the input. If the gain is 0, then this means that the output of the device is 0, regardless of the input. Finally, if the device has a negative gain, then the output will have an opposite polarity compared to the input. (As you go through this section, you should always keep in mind that a negative gain is different from a gain with a negative value in dB... but we'll straighten this out as we go along. (Incidentally, Lesson 2 for recording engineers, entitled ``How to wrap a microphone cable with one hand while holding a chili dog and a styrofoam cup of black coffee with 5 sugars in the other hand and not spill anything on your Twisted Sister World Tour T-shirt'' will be addressed in a later chapter.)