An improved instrumentation system has been developed to analyze the dynamic pressure field produced by jet aircraft. The system is automatic and utilizes analog computer techniques to obtain an accuracy of ±0.2 db in its readout. The method used is to secure a true rms value of octave band segments of the jet noise spectrum and to convert this to decibels by the use of a dc logarithmic amplifier. The transition to acoustical decibels is made by obtaining the difference between this voltage and another voltage obtained from a reference oscillator. The value of this reference oscillator in acoustical decibels is obtained by comparing its output voltage to that of a calibrated microphone. The dynamic range of the system has proved more than adequate for greater than 98% of the data processed by this unit during the time this system has been in operation. The output is in the form of punched cards for utilization with a digital computer.