All of that (which was quite interesting), yet he doesn't actually say what a decibel is. It is:
• 0.1 bel
• +/-1 bel = +/-10 dB = factor of 10 increase/decrease in power
• 0.1 bel
• +/-1 bel = +/-10 dB = factor of 10 increase/decrease in power
https://en.wikipedia.org/wiki/Neper
The Np seems to have be used for amplitudes (rather than power), and value/ref = e^Np. And 0.01 Np ~ 1.01 (+1%) which is probably less useful than it seems at first glance.
Although I am probably wrong, I always thought that "decibel" actually meant "decimal bel" because it represents a decimal logarithm and that the "bel" unit was devised as an afterthought to fit the SI prefix.
Still, it is a good way to remember that 10 dB = multiply by 10, because "deci" means 10.
It's named after Alexander Graham Bell, in 1928 at Bell Labs. https://en.wikipedia.org/wiki/Decibel#History (Yes I worked there, it was part of indoctrination training... :)
> because "deci" means 10.
Really, it means 1/10. ("Deca" is 10.)
Ah, but it is: https://www.hgst.com/products/hard-drives/ultrastar-he12 (click the "Specifications" tab and scroll down to "Acoustics")
(Hmm, this doesn't say what the reference level is. I guess it's 20μPa.)