Frequency-dependent limiters for FM sound broadcasting: Optimization of attack period and of delay-length in the variable de-emphasis stage

Following earlier experimental investigations on the problem of noticeable gain changes when conventional program limiters are used for FM sound transmissions, a variable-emphasis limiter arrangement was indicated as one solution. The arrangement comprised two limiter stages in cascade - the first regulating the level of the un-emphasized incoming program signals, and the second controlling, in a selective manner, the high-frequency input components raised above limiting level by pre-emphasis. In the original experimental equipment both stages were of a relatively complex design - each including a lumped-constant program signal delay network - to avoid momentary overshoot. Subjective tests indicate that the delay-line of the second stage may be omitted, with negligible program impairment, provided that certain simple precautions are taken. In particular, if the system demands no overshoot of any kind beyond certain limits that may set by a clipper at the output, the maximum steady-state output of the program limiter should be set below the clipping level by a margin of 0(75) db.