During the early decades of commercial broadcasting, amplitude modulation (AM) was the standard technology. AM radio works by varying the amplitude of the carrier wave in proportion to the audio signal. While simple to implement, AM signals are vulnerable to electrical interference from lightning, power lines, and household appliances. This interference causes static noise that degrades the listening experience, especially during bad weather or in urban areas with high electrical activity.
Engineer Edwin Howard Armstrong developed frequency modulation (FM) in the 1930s to address the static inherent in AM. Armstrong (1936) showed that by keeping the amplitude constant and varying the frequency of the carrier wave, the receiver could reject amplitude-based static. Additionally, FM supported an audio frequency response of 50 Hz to 15,000 Hz, a significant improvement over the 5,000 Hz limit of commercial AM radio. This wider frequency response allowed FM to reproduce music with much greater clarity and detail.
Armstrong's key insight was that using a wider channel bandwidth could reduce noise. This ran counter to the established engineering belief that narrowing the bandwidth was the only way to reduce noise. The FCC allocated 200 kHz channels for FM stations, which allowed for high-fidelity audio and the later addition of subcarriers. These subcarriers enabled stereo broadcasting and secondary services without interfering with the main audio program, making FM a versatile platform for commercial broadcasters.
The adoption of FM was delayed by corporate and regulatory disputes. Major networks with investments in AM infrastructure opposed FM. In 1945, the FCC moved the FM band from 42-50 MHz to its current allocation of 88-108 MHz. This change made all existing FM transmitters and receivers obsolete, slowing the technology's growth. However, post-war demand for high-fidelity music led to an FM revival. By the late 1970s, FM surpassed AM in listenership, and AM shifted to news, talk, and sports formats, illustrating how consumer demand for quality can drive technological change.
The transition of music to the FM band established high-fidelity audio as a consumer expectation. This demand for audio quality has continued into the digital age, influencing the development of streaming codecs and internet radio. Modern lossless and high-bitrate streams continue the work begun by Armstrong, delivering clear sound free of static to listeners worldwide, showing that the pursuit of audio quality remains a central theme in media history.
References:
Armstrong, E. H. (1936). A method of reducing disturbances in radio signaling by a method of frequency modulation. Proceedings of the Institute of Radio Engineers, 24(5), 689-740.
Lessing, L. (1956). Man of High Fidelity: Edwin Howard Armstrong. Lippincott.