What makes LED's different than other diodes?

[Caferacernoc]

I just received the AMZ cd, awesome by the way, and looking at the diode harmonics test I don't understand how LED's can generate even harmonics when set up for symmetrical clipping. No other diode can do that without being "mismatched" into assymetrical clipping. And everything I have ever read about distortion states that symmetrical clipping causes odd harmonics only. The fact that LED's can do this does explain why they sound good despite the fact that they actually have a pretty sharp clipping "knee". Anyway, I'm just curious about that even harmonics thing.
Thanks for any insight and thumbs up for the AMZ cd, tons of good stuff in there!

[amz-fx]

Thanks for your kind comments!

Hard symmetrical clipping will cause only odd harmonics but the clipping must be heavy so that the signal is essentially a square wave, which has only odd harmonics.

Symmetrical waves can have even harmonics, such as a sawtooth wave, which has both even and odd harmonics.

If the knee is soft, then there are most likely some even harmonics present.

The knee of an LED may appear sharp alongside a graph with a silicon diode but in actual practice with audio, the clipping is not as hard because of the higher threshold of the LED conduction, and this leads to a softer sound.

Bottom line...  lots of factors are impacting the sound, not just the type of diode.

regards, Jack