Hello -- I am not a big arranger, but I have arranged a handful of
tunes for the Raffin 20er crank organ.  (But I have not ever heard most
of them except on the computer, because I do not yet own an organ.)

Actually, I _love_ to arrange for this micro-scale of 20 notes.  Coming
from the full-scale piano and with a jazzy and classical-chromatic
background, I only learned with the 20er scale what tricks you can
play.  (Quite certainly, I found only a few of them up to now.)  Of
course, at times you have to "straighten out" things, but still,
e.g.  playing a "complete C scale" with a missing B (-natural) is fun.
(I do it by replacing the B with a G and having some other ascending
line that helps the listener "go up").

And regarding a much smaller scale::  On and off, I listen to
MIDI transcriptions of classical music by Ramon Pajares
(http://nil.es/rpajares/).  In August, he posted the overture to
Rossini's L'Italiana in Algeri, and, as I usually do, I listened
to any errors that might be in the transcription.  There was one:
In measure 63, the timpani are definitely one tone too low.  It
should be D, not C... Really??

After looking through the complete score, I found that this was
(almost) the only place where a D would be necessary.  Having a third
timpani only for a few measures is out of the question, so Rossini used
the C (which is part of D7 chord).  There are a few other places where
Rossini arranged "around the missing D":

  m.118..127      organ point
  m.131/135       D is simply left out
  m.174/175       replacement chord for quint

(I think this was/is called a "Neapolitanic", at least in German;
any musician out there who wants to correct me?)

And in m.166..173 one can see/hear how this single C can be "attached"
to four different harmonic contexts.

So much for a _very_ small scale.  The moral?  There are certainly
many, but three worth mentioning are:

(1) Not only organ arrangers have to cope with limited resources.
(2) Also a small scale can be used creatively.
(3) I'll never be a Rossini ...

Regards

Harald M. Mueller

 [ Well, then you might be a fine tympanist!   My little Dictionary
 [ of Musical Terms, of 1895, says: "Neapolitan sixth -- a chord of
 [ the sixth on the sub-dominant in minor, with minor sixth."  My, my!
 [ A "fifth of Scotch" is more entertaining!  :)  -- Robbie