Click here to purchase the entire book in PDF format. Amplitude The amplitude of a wave is simply an measurement of the height of the wave if it's transverse, or the amount of compression and refraction if it's longitudinal. In terms of sound, it's measured in Pascals, since sound waves are variation in atmospheric pressure. If we were measuring waves on the ocean, the unit of measurement would be metres. There are a number of methods of defining the amplitude measurement - we'll be using three, and you have to be careful not to confuse them. Peak Pressure - This is a measurement of the difference between the maximum value of the wave and the point of equilibrium. Peak to Peak Pressure - This is a measurement of the difference between the minimum and maximum values of the wave. Effective Pressure - This is a measurement based on the amount of power in the wave. It's equivalent to 0.707 of the Peak value if the signal is a sinusoidal wave. In other cases, the relationship between the effective pressure and the Peak value is different (we've already talked about this in Section 2.1.6 - except there, it's called the RMS value instead of the effective value). Figure 3.7: A sinusoidal pressure wave with a peak amplitude of 1, a peak-peak amplitude of 2 and an effective pressure of 0.707.