The Tektronix AA501 is a audio analyzer plug-in for the TM500 system.
It provides automated measurement of THD+N and levels (RMS responding) in the range of 10 Hz to 100 kHz. Harmonics are measured up to 300 kHz. It has four built-in weighting filters and allows the user to loop an external filter in. Option 01 adds intermodulation measurement. Input impedance is 100 kΩ and unlike other analyzers with usually 1 MΩ or near-infinite input impedance. Internal THD in the audio band is specified as typically <-95 dB (0.0018 %). Residual THD+N is specified as <-90 dB (<0.0032 %).
It was one of the first, if not the first, audio analyzer capable of fully automatic measurements without requiring manual reference level setting, range selection or frequency fine-tuning. It is ideally combined with the SG505 low distortion oscillator.
The AA501 is two slots wide.