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Increasing the Audio Measurement Capability of FFT Analyzers by Microcomputer Postprocessing
A fast Fourier transform (FFT) spectrum analyzer, especially a dual-channel device, can furnish increased measurement capabilities if its data can be sent to a microcomputer for postprocessing. Some of the additional capabilities that the authors have achieved are illustrated, their usefulness in audio measurement is discussed, and their theoretical basis and the means by which they are computed are outlined. The FFT analyzer, in addition to acquiring the data, functions essentially as a rapid Fourier transform calculator and flexible display unit, while the data are suitably reconfigured in the microcomputer and shuttled forward and backward between them. The computation is shown of 1) the analytic signal and its envelope (that is, the "energy-time curve"), 2) the minimum-phase and excess-phase portions of a system's phase response, 3) constant relative bandwidth smoothing (such as one-third-octave smoothing) of FFT spectral data, and 4) the cumulative spectral decay plot (that is, the "waterfall" plot of power versus frequency versus time).
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