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Years ago, AM broadcast stations began using audio processors that permitted at least 125% positive peak modulation (if the transmitter was capable of it). That helped to extend their coverage range at the fringes of their useful daytime groundwave signals.
They also began to use other audio processor settings that greatly increased the density, or average value of the audio waveform prior to modulation of the transmitter, while keeping positive and negative peaks of the audio waveform under tight control. Carried to an extreme, transmitter modulation rarely drops below about 125% positive, 99% negative (the present FCC limit on positive peaks for AM broadcast stations is 125%).
This greater density in the audio waveform actually has a much larger benefit than using +125% modulation toward improving the signal-to-noise ratio that a listener perceives in the audio output of an AM receiver. But it adds distortion to the program waveform, and can be tiresome to listen to for long periods of time, for some people.
Also – most people adjust the volume control of an AM radio receiver to a setting producing the acoustic sound level they want in that listening environment (car, living room, etc). This tends to reduce the effects of using highly processed audio at the transmitter in areas of high field strength from the AM station, except maybe to increase the “tune-out” factor. More benefit could be possible in the coverage area fringe due to noticeably better signal-to-noise ratio there at a given setting of the receiver volume control.