Increasing the Audio Measurement Capability of FFT Analyzers by Microcomputer Post-Processing
An FFT spectrum analyzer, especially a dual-channel device, can furnish increased measurement capabilities of its data can be sent to a microcomputer for postprocessing. This paper illustrates some of the additional capabilities which the authors have achieved, discusses their usefulness in audio measurement, and outlines their theoretical basis and the means by which they are computed. The FFT analyzer, in addition to acquiring the data, functions essentially as a rapid Fourier transform calculator and flexible display unit, while the data is suitably reconfigured in the microcomputer and shuttled forwards and backwards between them. We show the computation of a) the analytic signal and its envelope (i.e., the "energy-time curve"), b) the minimim-phase and excess-phase portions of a system's phase response, c) constant relative bandwidth smoothing (e.g., 1/3-octave smoothing) of FFT spectral data, and d) the cumulative spectral decay plot (i.e., the "waterfall" plot of power vs. frequency vs. time).
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