After the information about the user is measures by a sensor, it must be changed to a form appropriate for input into the data acquisition system. In most applications this means changing the sensors output to a voltage (if it isn't already), modifying the sensors dynamic range to maximize the accuracy of the data acquisition system, removing unwanted signals, and limiting the sensor's spectrum. Additionally, analog signal processing (both linear and nonlinear) may be desired to alleviate processing load from the data acquisition system and the computer.
Section 4 below discusses some signal conditioning circuits as they apply to particular sensors. The correct design of the signal conditioning system is critical in mapping the sensor output to the data acquisition input. Incorrect choices can affect the way the computer reacts to the human input. Thus, it is important to note the changes in the properties of the sensor signal caused by the conditioning circuitry.