Hewlett Packard 334A Distortion Analyzer measures total distortion down to 0.1% full scale at any frequency between 5 Hz and 600 kHz; harmonics are indicated up to 3 MHz. Noise levels as low as 25 microvolts can be measured. The HP 334A includes automatic fundamental nulling and amplitude modulation detector. A meter with VU ballistic characteristics, and a 30 kHz low pass filter are optional.