The title says it all. I’ve just begun studying CCNA and everything I thought I knew about decibels (the prior musician side of me obviously correlated it with sound) was thrown out the window when I learned that it was also used to measure electrical signals. I’ve been trying to read wikis but none of them really hit on how it can measure both sound and voltage, which are two completely different things…
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decibels are just a convenient way to refer to things with a wild range. Every dB set you encounter is going to have a baseline reference for it.
For sound we use dB spl (sound pressure level) because sounds pressures range from variations of 20 micropascal (threshold of hearing) to 100 kPa (191 dB, above this its a shockwave). The reference for this is 20 micropascals which is the threshold of human hearing (around 1 kHz)
For antennas a lot of work is done in dBm which is referenced to 1 milliwatt of power sent/received by an antenna. Some small signals may be measured as dBuV (decibel microvolts). These are useful measures because your real value could be anywhere from the Mega to the Femto range for antenna power and since a lot of channels will half your power you get to just subtract 3 or 6 dB(depending on power or voltage) instead of dividing weird numbers over and over again.
dB are a cheat for systems with massive dynamic ranges
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