The General Radio 1564A Sound/Vibration Analyzer operates in the frequency range of 2.5 Hz to 25 kHz in four decades. 25 Mohms input impedance in parallel with 80 pF. Input range of 0.3 mV to 30 V full scale. Output: 1 V open circuit. Three scales: 0 to 3 V, 0 to 10 V, -6 to +10 dB. AC or battery operated. Unit comes with 2 microphones.