Consumer Electronics

PRE-EMPHASIS AND DE-EMPHASIS

In frequency modulation the modulation or sideband frequencies often extend outward to as much as 15 kHz. This provides a much broader audio range than is usually found in conventional A.M. broadcasting. The higher audio frequencies produced by the program source are generally weaker than the lower audio frequencies, and thus produce a smaller frequency deviation in the carrier. In the normal transmitting process a certain amount of interference is encountered, such as atmospherics, which have little effect on the large amplitude low-frequency signals. However, with regard to the weak high-frequency signals, the signal-to-noise ratio is low. To correct this condition, the Federal Communication Commission (FCC) standards ...