Amplifiers Can Introduce Noise and Distortion

Amplifiers are kind of like speakers. Some are really good at boosting signals that represent certain frequency ranges, and not as great at other frequency ranges. Higher numbers indicate that the amplifier is more prone to introducing unwonted signal. So if you ever are looking at hifi equipment and you find that there's a number that represents total harmonic distortion plus noise, you want that number to be aso o as it can be. The lower that number, the better it is.