Recording seismic waves without phase distortion

Claim 1

A SIGNAL CHANNEL HAVING INPUT TERMINALS AND OUTPUT TERMINALS, CIRCUIT ELEMENTS, BETWEEN SAID TERMINALS CONNECTED TO FORM A FILTER FOR TRANSMISSION TO SAID OUTPUT TERMINASL OF A BAND OF SELECTED FREQUENCIES OF THE SIGNAL APPLIED TO SAID INPUT TERMINALS AND FOR REJECTING OTHER FREQUENCIES, SAID FILTER HAVING A NON-LINEAR PHASEFREQUENCY RESPONSE CHARACTERISTIC, CIRCUIT MEANS BETWEEN SAID TERMINALS RESONANT AT A FIRST FREQUENCY IN THE NONLINEAR PORTION OF SAID PHASE-FREQUENCY RESPONSE CHARACTERISTIC FOR MODIFYING SAID PHASE-FREQUENCY RESPONSE CHARACTERISTIC BY A SELECTED INCREMENT AT SAID FIRST FREQUENCY, MEANS ASSOCIATED WITH SAID CIRCUIT MEANS FOR CONTROLLING THE RATE OF VARIATION OF THE MODIFICATION OF SAID PHASEFREQUENCY RESPONSE CHARACTERISTIC AT AND ADJACENT SAID SAID FIRST FREQUENCY TO ELIMINATE CURVATURE OF SAID PHASEFREQUENCY RESPONSE CHARACTERISTIC AT AND ADJACENT SAID FIRST FREQUENCY AND A CORRECTIVE NETWORK BETWEEN SAID TERMINALS INTRODUCING A PHASE ANGLE CORRECTION OF MAGNITUDE CONSTANT FOR ALL FREQUENCIES OF SAID BAND FOR CONTROLLING THE ZERO-FREQUENCY INTERCEPT OF THE PORTION OF SAID PHASE-FREQUENCY RESPONSE CHARACTERISTIC AT AND ADJACENT SAID FIRST FREQUENCY.