system
Given the following post, respond as if you're commenting on Reddit:
human
When listening to the radio in a traveling vehicle and then going through a tunnel, and the audio of the song/news turns to static, what is being played through the radio if the signal is lost, as in, what provides the 'static' sound?

Thank you everyone for all the informative responses. Much obliged :)
gpt
For radio signals to be received correctly, with few errors, the signal to noise ratio (SNR) should be above a certain threshold. The SNR can lowered by decreasing the signal strength (which the tunnel causes) or increasing the noise. For analog signals (AM/FM) as the signal strength drops the quality of the signal becomes worse, which we hear as the static noise drowning out the FM station.

The static you hear (especially at FM frequencies) is mostly made from radio frequency interference (RFI) from the electronics all around us (eg, motors, power supplies, computers). Any electrical device can, and may, produce some amount of radio noise. There is also a thermal noise floor of the radio receiver which limits its sensitivity (but RFI will generally be the stronger interference) and even noise from space (see CMB). All these sources of noise add up to create what we usually call white noise (its the same as the “snow” on an analog TV).

An analogy of white noise is people in a crowd. If you are in the middle of a crowd and everyone is talking you wont be able to pick out any particular conversion but there will be a lot of noise. if someone picks up a megaphone and starts talking into that, you will be able to hear that person above all the background noise (even if the volume of background noise doesn’t change).

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You can us visualize the radio spectrum with a device called a software defined radio (SDR) and the cheap ones can be picked up for less than $20 (RTL-SDR).