Is the effect of harmonic distortion which is impactful on sine-waves actually visible in square-waves?
Square waves would mostly show odd order distortion, if at all. But frequency response would change their shape way more, so they're not really that useful, except maybe for subbass to show the slew rate equivalent of the device and bass sustain. You would see rounded for boosted slow bass, falling for poor sustain and ringy for artificially fast. Best would be of course level without ringing.
I'm talking e.g. 50 Hz square wave. Subbass behavior is not really visible on CSDs and dynamic behavior is not visible on the FR chart.
