Audio amplifier whose output amplification rate of change is less than its input signal amplitude rate of change. While compressors are used to reduce the dynamic range of program signals either to make everything sound louder, or to automatically control sudden large changes in signal amplitude such as in the case of recording vocalists, limiters are used to prevent dynamic transient signal peaks from exceeding a pre-set amplitude. Limiters are usually required when broadcast signals are fed to telephone lines and are useful to prevent power amplifiers clipping and overdriving in large sound systems. Limiters sometimes include circuits that allow the user to adjust the time it takes to start reducing the signal amplitude (attack) to ease up on the compression (release), and also the input and output gain.