He "drags" tones by pressing the keys very slowly, and this is a technique which is systemic really not part of the classic organ building; to generate a constant and reliable sound that organ pipe needs a constant air pressure, so there is not a glissando on the organ and no quarter tones.
Many organists have with mechanical tracker action also tried on their instruments (what that is: [...]) to generate, quarter tones or glissandos. But they then quickly determined that this was not reliable and tonal consistently works in a pipe register and certainly not with different registers - and that's why they have it quickly down his back.
This Riepp organ here forms a very unusual exception: It works for this instrument in individual registers, and as Keith Jarrett does not know what "it" as an organist does or does not do, he plays simply.
The special value of this recording is for me exactly in this meeting of an instrument of world renown with a musician (also a world-class), the lures out of the instrument sounds, it really should not be ...
