system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do Spectrum analyzers work, what is their real world application and why are they so common with "ghost hunters"?
gpt
Spectrum analysers often work based on something called the Fast Fourier Transform.

This is a mathematical technique which lets us look at a wave, let's say the sound of a lion's roar, and instead of looking at how it changes over time (like having a loud beginning, slowly getting quieter, and a few grumbles at the end), asking what other waves it is made of.

That feels like a big jump, but it's simpler than you think. Sticking with sound, you may know that the pitch of a sound is determined by something called it's frequency. This is mostly true, but it's not the full picture. Sounds are made up of lots and lots of frequencies all added together. This is what makes a violin sound different to a flute if they're playing the same note. What this means is that if you take a very simple wave which genuinely only has a single frequency, called a sine wave, and start adding very special amounts of other waves of very specific frequencies, you can actually build sounds from scratch - this is called "additive synthesis", by the way.

What the Fast Fourier Transform does is tell you exactly what amount of *all* frequencies have gone into making whatever wave it's looking at. This is sometimes called a "decomposition", because it is looking at what the wave is composed of.

Why is it associated with ghost hunters? Because they need some bullshit to hook people's attention and these things look cool and technical and a good storyteller can make a story out of it.