Digital-to-analog converter (DAC) chips transform information from digital to analog form. They convert signals that have two defined states, on and off, into signals that have a theoretically infinite number of states. For example, modems convert digital computer data that consists of ones and zeroes into audio frequency (AF) tones that can be transmitted over telephone lines. Digital-to-analog converter chips are also used in digital signal processing to improve the intelligibility and fidelity of analog signals. First, analog-to-digital converter chips (ADCs) are used to convert analog signals into digital form. Next, special circuitry is used to improve these signals. Finally, digital-to-analog converter chips are used to transform the digital impulses back into analog form.