What is the difference between dB and dBA?

The dB scale is used to measure sound level. However, because the human ear does not respond equally to all frequencies, we often use dBA as a scale of measurement. This is an adjusted measurement of noise that takes into account the sensitivity of the human ear to the various sound frequencies which we can hear. Certain frequencies irritate more than others. As an example, think of fingernails dragging across a blackboard.