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While one reason for limiting the audio bandwidth to 4.5 kHz was to allow a great enough number of channels in the long wave and medium wave bands, the second r

While one reason for limiting the audio bandwidth to 4.5 kHz was to allow a great enough number of channels in the long wave and medium wave bands, the second reason was to be able to reject the high frequency noise by low-pass filtering. So there were two reasons for the low audio fidelity of AM broadcasting, and noise was one of them, with the contention between multiple broadcasters for the narrow available bands being the other.

giantrobot 2y ago
> with the contention between multiple broadcasters for the narrow available bands being the other. A non-obvious aspect of medium and long wave AM broadcast is depending on weather/atmospheric conditions a signal can propagate much further than its output power would suggest. This means a distant station on the same channel as a near station may end up in contention at certain times of day or random conditions. Solar flare? Suddenly stations a hundred miles away are overpowering local stations or just adding a lot of noise. Medium and long wave is also susceptible to local EM sources like switching power supplies and electric motors. So you can get the double whammy of local noice and distant stations adding additional interference to local stations.