The AA501A Distortion Analyzer provides fully automated measurement of level, total harmonic distortion plus noise (THD+N). Operation is made simple, select the mode and the rest is automatic! Fundamental frequency range is 10Hz to 100kHz, with harmonics measured out to 300kHz. Allows readings to be expressed in true RMS or average response. Any one of four built-in frequency-weighting filters may be switched into the signal paths for preconditioning of the signal to be measured. Provision is also made to permit the use of a user-selected filter as well. Other features include input monitor, function output, and auxiliary input connectors.