What device did Edwin Armstrong invent in 1933 that greatly improved radio sound quality?

Early radio broadcasts, primarily using Amplitude Modulation (AM), were often plagued by static and interference. Electrical storms, car ignitions, and even household appliances could disrupt the signal, leading to a noisy and often frustrating listening experience. The audio quality was limited, and listeners frequently contended with crackles and hisses that obscured the intended sound.

In 1933, the innovative American electrical engineer Edwin Howard Armstrong introduced a groundbreaking solution: Frequency Modulation, or FM radio. Armstrong's invention completely changed how radio waves carried sound. Instead of varying the amplitude (strength) of the radio wave, as AM did, FM modulated the frequency of the wave to encode the audio signal.

This ingenious shift dramatically improved sound quality. Since most electrical noise and static primarily affect the amplitude of a radio wave, FM signals became largely immune to these disturbances. The result was a remarkably clearer, richer, and more consistent sound, offering high-fidelity audio transmission that was a significant leap beyond AM. While initially facing resistance from established radio networks, FM radio eventually became the dominant method for high-quality audio broadcasting, transforming the listening experience for millions.