This circuit is used to convert a mono audio signal into a stereo signal that can be panned between the left and right channel by a 0-10V control signal, it is intended for analog synthesizer systems.source

This Sallen-Key realization of a 5.25-MHz, three-pole Butterworth filter has a gain of 2V/V and can drive 75Ω back-terminated coax with an overall gain of 1 .It can used to reconstruct component-video (Y, Pb, Pr) and RGB signals, this filter has an insertion loss greater than 20 db at 13.5 MHz and greater than 40 db at 27 MHz . Like the antialiasing filter before an ADC, this filter removes the higher frequency replicas of a signal following a DAC. To preserve quality in the video waveform, you should minimize group-delay variations in the filter and any group-delay differential between filters.source