| Abstrakt: |
A study has been made of the applicability of correlation techniques to the field of acoustic measurements. The development of an analog electronic correlator for this study is reported here while the application of the correlation technique to some acoustic measurements is reported in a companion paper. The analog correlator is divided into the following four main components and each one is discussed in detail: (1) variable time delay; (2) quarter-squaring multiplier; (3) continuous and stepping integrators; (4) system for scanning and plotting the crosscorrelation function on both linear and logarithmic scales. The correlator operates over an input frequency range of 100 cps to 10 kcps, a range of relative time delay τ from -15 to 190 milliseconds and RC integration times of 0.5 to 16 seconds. A dynamic range in the crosscorrelation function of approximately 50 db is achieved with ±1 db accuracy. Special attention has been given to the errors in the crosscorrelation function resulting from finite integration time and scanning of the correlation function. A significant increase in permissible scanning speed for a given signal-to-noise ratio has been shown to result from 'matching' the equivalent integrator pass band to that of the spectrum common to the two signals applied to the correlator. Relations have been derived between scanning speed, signal-to-noise ratio, and input signal band width for integration performed by either a low-pass filter or a "matched" filter. [ABSTRACT FROM AUTHOR] |
