DB of sound volume in relation to 20 micropascal weighted, simulating human ear sensitivity at 40 phon level. Note 1: 20 micropascal is the human hearing threshold, i.e., 0 dB (A. ) Note 2: Sound volumes louder than dB (A) are represented by a graduated scale: dB (B,) dB (C,) and dB (D. ) Note 3: This scale is widely used in occupational safety and hearing protection measurements.