Stereo Limiter

A limiter is an electronic volume adjust- ment circuit in which AF signals are amplified up to a predefined level of the input amplitude. When this level is reached, the gain of the amplifier is re- duced to ensure that a fixed, maximum, output level is not exceeded. In other words, the output amplitude remains constant irrespective of fluctuations of the input signal above the limiting threshold. Limiting is, therefore, often referred to as dynamic range compres- sion. Figure 1 shows the dynamic response-U0 as a function of U- of the proposed limiter. The design described here is based on a pair of standard gain controlled amplifiers which ensure a dynamic range compression of about 46 dB. The limiting threshold is reached at an input voltage of about 50 mV: the output voltage is then about 670 mV. Circuit description With reference to the circuit diagram of the stereo limiter in Fig. 2, opamp Ai sums the signals applied to the L and R inputs, and provides the gain control si...