The condenser type of pressure pick‐up for a high speed engine indicator has advantages of simplicity, ruggedness, and frequency response over other types. As used ordinarily, with a d.c. polarizing voltage, fidelity at low frequencies requires the use of a very high impedance input circuit, with consequent troubles from poor stability, low sensitivity, and particularly ignition pick‐up. The latter has required the use of airplane type shielding on ignition systems. These difficulties have been completely overcome by use of a high frequency (several megacycles per second) ``polarizing voltage'' in conjunction with a special bridged T type of balancing circuit. The T elements of this circuit can be built into the pick‐up very simply and ruggedly, thereby eliminating difficulties with capacity changes in the lead wires. The sensitivity of the circuit is such that very little amplification is required. Frequency response is limited only by the elastic characteristics of the diaphragm. Both pressure‐time and rate of pressure change‐time cards can be observed and photographed. The wide frequency response of the indicator makes it particularly applicable to the study of knocking combustion.