Portable audio test set incorporating an oscillator, frequency counter, db meter and impedance meter.A current controlled, state-variable true sine wave oscillator incorporating a fast AGC circuit. Distortion components are typically 0.1% 2nd and 0.05% 3rd which are low order and not audible making the TS1 & TS2 useful in making listening tests where a function generator would generate undesirable, audible side effects. Full frequency sweeps can be made from 20Hz - 20kHz in a single range. These units have no amplitude changes over the entire frequency range.The frequency counter is internally connected to the internal oscillator and displays the oscillator frequency until a signal is plugged into the input connector. It then displays the frequency of the input signal. This unique combination allows absolute precision in setting frequencies.