Audio output is at 5k ohm resistor in center. Equal amplitudes on microphones of roaring crowd (1 kHz.) enter both sides of differential amplifier. Note: amplified crowd roar amplitudes is equal on both sides of audio output (5k ohm resistor) stopping current flow of crowd sounds. Sitting in the stands you sports cast the game with your 400 Hz. microphone input which uncanceled from right amplifier is left for audio out. I used 5k ohm resistor as audio output transformer did not work for simulation.
