A three-component, broad-band seismic system which records directly onto seven-track digital tape is described. A novel approach of synthesizing a desired response by a differential filtering and summing technic using low-noise operational amplifiers is demonstrated. As an example, the usable velocity sensitivity of a Willmore Mark II seismometer having a natural period of 1.5 sec is extended out to about 40 sec under normal operating conditions. Seismic energy over a wide spectrum may thus be recorded.

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