Check left and right audio channels online. Play a generated test signal to identify the left and right headphone, or upload an audio/video file to inspect peak level, average loudness, balance, mono, duplicated mono and nearly identical stereo.
Useful when you need to confirm that headphones are worn correctly and left/right channels are not swapped. A high correlation close to 1.0 often means both channels are nearly the same. A strong balance offset means one channel is louder than the other.