True rms—The Digital Approach Free

Acoustical data typically extend over an extremely wide dynamic amplitude range, because of either source amplitude variations or of power spectral variations. Furthermore, it is highly desirable to afford the luxury of an amplitude range surplus to allow for the unknown level of a source that is to be measured. Digital detection can now provide a 70‐dB input dynamic range plus true rms performance with simultaneous multiple‐channel operation. This capability is made possible by the integrated circuit and by breakthroughs in the design of computational algorithms that are needed to perform rms calculations. Many analog devices have been built in the past to approximate such performance, but none can come close to the results obtainable with a straightforward digital approach. By performing the nonlinear operations of squaring and decibel conversion digitally, accuracy and dynamic range problems are greatly alleviated. Many other advantages also accrue, such as multiple‐channel operation and flexible control of the averaging or measurement interval, and will be discussed.