The main rule for choosing the best left hand fingering is to apply arpeggio or broken chord fingerings. Arpeggios of chords in the root position are played using 5 3 2 1 fingers. If the third is major between the two lower notes as in A flat C, play 5 3. If the third is minor as in F A flat, play 5 4. The chords of the first inversion are played using 5 4 2 1 fingerings and 5 3 2 1 are best suited for the second inversion chords.
Try to avoid placing the thumb on the sharp keys in the right hand part. However, it will not be always possible since the key of this chorale prelude has four flats. Play the ornaments using 4 3 fingers of the right hand.
As in most Baroque compositions, apply toes-only pedaling in this piece. Since the bass line is pulsating it will not always be possible to use alternate toe technique. However, in measures 4, 8, and 14 alternating right and left pedaling works well. You can treat the descending passage with repeated notes in measures 11 and 12 as a scale-like passage and play with alternate toes. Play with the same foot notes that are repeated and notes with change of direction.
Although the traditional way of articulating Baroque music is with articulated legato, you can see the slurs every four notes in the left hand part. This legato articulation is original and you should try to play all four notes legato. Make sure there are delicate breaks between the note groups. Play all notes with a gentle articulation in the right hand part and in the pedals except in measure 3, where the appoggiatura in the soprano should be slurred.
Ornaments in this chorale prelude should be played from the upper note. Because it is a very gentle and expressive piece, do not rush your ornaments and do not allow them to sound virtuosic. Try to maintain the elegant intimate character even in playing the faster notes. Do not play the ornaments automatically in the precise rhythm. They will sound more natural if you hold the first note of the trill or the mordent longer and play the remaining notes a little faster.
If you want more information about playing ornaments in the Baroque music, an invaluable resource is "Performing Baroque Music" by Mary Cyr which I highly recommend.
Although the practice keeping in mind the above points about fingering, pedaling, articulation, and ornamentation requires significant amount of patience and attention to detail, the results achieved by such a practice will be great because you will be able to perform “Ich ruf zu Dir, Herr Jesu Christ” with precision, clarity, and confidence.
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