Geo‐acoustical and geomagnetic data gathered by an array of sensors for long periods of time were recorded on magnetic tape in frequency‐modulated form. A new digitizing system was worked out for an accurate study, then data were reduced and adjusted (or “recolored” in the time domain) using a numerical‐analysis technique, which corrects for frequency attenuation due to the frequency‐response characteristics of the sensor and field recording equipment. Wavelength and wave velocity depended on frequency and statistical error estimated from study of the F‐1 engine. The mathematical techniques involved in recoloring and filtering are explained, and the statistical techniques (autocovariance, cross covariance) used in the time‐series analysis are discussed.