Pronunciation ˈdesɪbel

A unit of relative intensity or amplitude. Usually abbreviated to dB. When dealing with intensity ratios the decibel is defined by the formula 10 log(I₁/I₂), where I₁ and I₂ are the intensity values of the two sounds concerned. For amplitude ratios, the formula is 20 log(A₁/A₂). A₁ and A₂ are the amplitude values for the two sounds. For the measurement of speech sounds, the unit dB IL (Intensity Level) or dB SPL (Sound Pressure Level) is often used. In this case the I₁ or A₂ is the intensity or amplitude of the speech sound concerned and I₂ or A₂ is a reference representing the intensity level 10^-16watts/cm²) or amplitude value (0.0002 dynes/cm²) of the threshold of human hearing. On this scale, normal conversation has a level of approximately 60dB, shouting or singing a level of about 75dB and a sound loud enough to cause physical pain a level of about 130dB.