The most likely explanation I know that fits all the facts is a Schumann generator adds dither, and this improves our aural perception of sound the same as it improves our visual perception of images.i was thinking so in a way analogous to a kind of mechanical dithering effect but in the electromagnetic dimensions where the fine line imposed by the ratio signals/noise emerged audibly ...
The reason why i was thinking so it that the S. G. without modification add acoustically something to the listener envelopment experience and to the relation between imaging and soundstage...
But when i was experimenting with shungite i was really surprized to observe the compression of the sound when i put the shungite only on the capacitors...
When i tried with only herkimer diamond the effect was opposite: a decompression... In the 2 cases it was not always ideal musically but when i added the 2 together there is a balancing very optimal musical effect... Especially when i transformed the shungite with copper tape in what i called a "golden plate"...
Then the S.G. act on the electrical grid itself of the room and gear not only like a dithering effect...But i am not a scientist for sure...