INSTRUMENT WHICH IS A SUB-AUDIO AND AUDIO SPECTROGRAPH WHICH PRODUCES PERMANENT VISUAL RECORDS SHOWING DISTRIBUTION OF SIGNAL AMPLITUDE, AS TO BOTH FREQUENCY AND TIME. IT IS USEFUL FOR STUDIES OF TRANSIENT AND STEADY STATE SIGNALS ON AIRCRAFT, SHIPS, ROTATING AND RECIPROCATING MACHINERY AND IN FIELDS SUCH AS ORDNANCE, BALLISTICS, SEISMOLOGY, AND ACOUSTICS