For now, you may be right, since my recent interest on Bach was mainly awaken by my frustration from the quite unsuccessful practicing of that Bach-Rach piece. I practiced and practiced, but I can hardly see any technical improvement between the recording in my last post on AR and my playing now. At first I thought I have to include some etudes in my daily practicing. But which etudes? Then it occurred to me it could be a Bach, Bach in original.
Ah that was the trigger, I see. Well, I think it's normal that a difficult piece cannot be mastered the first time you approach it (at least, that is what happens to me everytime). When you feel that there's no further improvement on a piano piece, it is time to give it a rest, especially if you have been working exclusively on it.
Re which etudes can be useful to reinforce the kind of technique required by that transcription I recommend: some of the 2 Clav.variations from the Goldbergs (ex: V, XI, XIV, XVII, XX, XXIII, XXVI), some Scarlatti sonatas with jumps and crossings like the K.28 (but there dozens with jumps and crossings).
The word "finger substitution" caught my attention! I usually use that technique to play flowing legato. In what kinds of situations could it be applied on Bach? And do you mean by "finger crossing" here just that of 4th and 5th fingers or are there another cases?
Finger substitution/changing on the same note is ubiquitous in Bach's keyboard music, particularly in the contrapuntally denser works. But you can use it every time you must or want to keep the music clean of the pedal. Finger crossing is when a finger of 'lower numeral' crosses over a finger of 'higher numeral' in a direction away from the thumb or viceversa (a 'higher' finger over a 'lower' one towards the thumb). It's very useful to obtain an otherwise unachievable legato and, in many cases, I prefer it to 'thumb under' in order to keep the hand perpendicular to the keyboard. Both finger substitution and finger crossing are helpful when you 'run out' of fingers and cannot or don't want to employ the thumb. The finger crossing piece par excellence is Chopin's Etude Op.10/2 of course.
Look at these 2 examples of finger crossing from the Bach-Rach Gigue (the second one is my fingering, probably others would put the thumb on the E#).
That is what I usually do. But you know, I find very often my inner clock is disturbed by the fright in front of the recorder! Once I turned on my digital metronom in "mute" (so that I can only "see" the beats") and restarted recording the same thing. And the result was much better. But somehow I felt as if I'm cheating... I don't know...
I don’t think it’s cheating, but a bit bewildering (me).
The easier Chopin pieces did not in any way prepare me for the more difficult Chopin pieces
Well, this is true for every composer, isn't it? However what's really remarkable in Chopin is that virtually all the difficult passages in his music are entirely included in his 2 sets of etudes. Only Scriabin, to an extent, did something like that.
The prelude introduces a technique that Chopin was very fond of, because Chopin was enormously fond of functional counterpoint, but he had either a distaste for writing strict counterpoint or an insecurity complex about writing it (which would be understandable, in the face of Bach...Bach leaves the impression that any attempt on our part to do what he did with strict counterpoint would be, at best, redundant).
No biedermaier or early romantic composer would have possibly written music in the strict style à la Bach (apart sometimes Mendelssohn, clearly an exception). In the best case, the goal was to assimilate the techniques of the old masters, blending them in a new style.
Alf mentioned the WTC as didactic works, but the suites and the Goldberg variations were all published under the title Klavier-Übung
Don’t mix up the original destination of those works in their aesthetic frame of reference with the didactic use that piano teaching has historically made of them. Bach published the Partitas as (the first volume of the) Clavier-Uebung after Kuhnau’s C-U, itself a collection of suites in 2 volumes. The ‘Uebung’ here is a concept that has more to do with the composer activity than the player’s.