AM vs FM Radio: What’s the Distinction?

Thanks to the digital age, Generation Z doesn’t spend much time adjusting a radio dial in hopes of hearing their favorite track. But for Millennials and earlier generations, the experience—and the terms AM and FM—are definitely familiar.

You likely know that AM and FM refer to different types of radio stations. But how are they actually different?

To understand this, it’s helpful to have a basic grasp of how radios generate sound in the first place. Every radio station sends out what’s called a carrier wave or carrier signal, which is essentially a constant electromagnetic wave whose properties—such as frequency and amplitude—remain unchanged. That is, until a DJ starts playing a track (or any other audio is broadcast). Those sound waves are converted into electrical signals, transmitted through the carrier wave to your radio antenna, and then turned back into sound waves that your speaker emits. The carrier wave alters in one of two ways while transmitting these signals.

On AM radio stations, the carrier wave’s amplitude—the height of the wave—varies according to the signals. As Soundfly’s Flypaper explains, this process is called amplitude modulation, hence the AM. In contrast, FM radio stations keep the amplitude constant, but the frequency—the number of complete wave cycles in a given period—fluctuates.

FM stands for frequency modulation, and is generally considered superior to AM. When random electrical interference disrupts a carrier wave, it can alter its amplitude. Since FM waves don’t rely on amplitude to transmit signals, as PBS explains, the signal quality remains unaffected by this interference. However, changing the amplitude of an AM carrier can distort the data it’s carrying, which is why AM radio often has more static. FM radio also spans a broader frequency range—known as bandwidth—which allows it to carry a wider range of sound details. If you’re broadcasting music, FM will provide better sound quality.

That being said, AM radio does have its perks. As noted in the video above, AM’s wavelengths—the distance between wave crests—are much longer than FM’s. This allows the signal to travel farther and maintain integrity even when it encounters obstacles like buildings or mountains. If your goal is to reach the widest audience, AM radio might be the better choice.