It can cause nausea and diarrhea, especially in high doses or after long-term use. It might also pose a risk of ulcers in high doses. As a topical treatment, it can cause skin irritation. Caution is advised when turmeric is taken by people known to have gallstones; consult your health care provider first.
Gain is the ratio between the magnitude of output and input signals. Gain controls on an amplifier are basically just small potentiometers (variable resistors) or volume controls, that allow you to adjust the incoming signal to the amplifier.
As dB is a relationship between two signals we'll first need to establish a reference point to which we can reference our dB scale. A handy reference is dBm which is the signal level in dB relative to 1mW. 0dBm is simply when the injected voltage causes a load to dissipate 1mW. But this still does not give us a voltage, multimeters cannot measure power.