mixer either of two electronic devices in which two or more signals are combined. In the type of mixer used in radio receivers, radar receivers, and similar systems, a signal is translated upward or downward in frequency. The basic property of such a device is that its output is not directly proportional to its input, but to the product of its inputs; when signals of different frequencies are applied to such a device, the output contains not only the original frequencies but also frequencies equal to the sum and difference of the original frequencies. Desired components in the output can be separated from the others by a suitable filter, and any modulation present on one of the input signals is preserved on the output. In the type of mixer used, for example, to combine the outputs of several microphones into a single channel, several signals are combined to produce an output proportional to their sum. Each of the input signals usually passes through a potentiometer or similar control that fixes its relative level in the output. Signals can also be mixed using digital techniques.