Ubiquitous Analyzers—Theory, Operation, and Performance
H. J. Bickel, Arthur Citrin, R. Vogel · The Journal of the Acoustical Society of America · 1970
Ubiquitous analyzers compute 10 000 to 50 000 spectral points per second using time-compression techniques. Analog input signals are band limited prior to sampling and quantization. Time series of 1500 nine-bit words are processed to yield 500 or more spectral points in 50 msec. Sampling takes place at 1.5×Nyquist frequency with a 300-kHz upper limit in current equipment. The width of the analysis range is one-third the sampling frequency, and the processing bandwidth is 1/500 the analysis range. Signal storage and time compression are carried out digitally, while filtering takes place in the analog domain. The filter shape is controlled by convolving the time series with a window function. Ubiquitous analyzers are building blocks in systems performing cross-spectrum analysis and correlation. Mean-spectral characteristics are obtained with a digital averager following spectrum analysis. For spectral-density measurements, absolute calibration is established in terms of volts2/Hz. The equipment offers a choice of estimating spectral density, using an rms-type detector, but superior dynamic range (better than 10 000/1) is realized with pseudo-rms detection.