A. Signal Generation. This category includes devices to generate signals, as well as devices which reproduce signals from some form of storage. Microphones make use of a transducer, which responds to air-pressure changes by creating an analog electrical signal. Microphone signals are typically low-voltage, and often balanced. This may be a stand-alone device, or is often part of a piece of equipment such as some tape decks, or, more commonly, a mixer.
Microphones known as condenser microphones require a power source in order to operate.
This is sometimes a battery, especially in inexpensive models. The mixing board or a dedicated phantom power supply are the source of this signal. Sound playback devices include turntables, CD players, radio tuners, and tape decks. All of these retrieve signals from some storage medium. If the signal data are digital, they can either be transmitted digitally, or converted to an analog signal.