The output goes high for a brief moment when any of the inputs change state. All four inputs change at a different frequency:
Top - Quarter note at 8000 BPM (7.5 ms)
2nd Top - Dotted eighth note at 8000 BPM (5 ms)
2nd Bottom - Triplet eighth note at 8000 BPM (2.5 ms)
Bottom - Quintuplet sixteenth note at 8000 BPM (1.5 ms)
