This chapter examines the link between the signals one measures and the physical wave or energy that is being measured by a sensor, or generated by an actuator. It considers the signal conditioning and transmission from the sensor in order to properly characterize the signal information and background noise. Pulse width modulated signals are read using a very high-speed counter that allows the time between and duration of square pulses to represent the sensor signal message. Acoustics and vibration sensors are really only a small subset of sensors, but they are by far the most interesting insofar as magnitude and phase calibration of wideband signals, transducer physics, and environmental effects. The electrostatic transducer is commonly used for wide frequency response condenser microphones, accelerometers for measuring vibrations over a wide frequency range, force gauges, electrostatic loudspeakers, and in sonar and ultrasonic imaging.