This document discusses pre-emphasis and de-emphasis in analog communication systems. Pre-emphasis is used at the transmitter to boost higher modulating frequencies, reducing noise effects. It involves passing the audio through a high-pass filter. De-emphasis is used at the receiver to remove the boosting, involving a low-pass filter. Both use time constants of 50 microseconds according to standards. Pre-emphasis increases modulation index for higher frequencies while de-emphasis removes this at the receiver.