Octaves are difficult to play because the thumb is the strongest digit and the fifth finger is
the weakest. Double octaves, that is, octaves in both hands at the same time, are more
difficult still, especially in fast passages, whether loud or soft. A pianist with a wider
stretch and more suppleness is able to play octaves with the thumb and the fourth finger.
In melodic octaves the fifth can alternate with the fourth, and even the third as
recommended by Liszt.
Chopin wrote an étude for double octaves, opus 25 no. 10 in B minor, but he does not
usually require double octaves in his piano music. Liszt wrote many double octaves in
his piano concertos and in his Sonata in B minor and other piano works.
ORNAMENTATION
In Bach the mordent is a three note ornament consisting of the main note, the note below
and the main note again.
In Bach the short trill/inverted mordent used to be viewed as a three note ornament
starting on the main note but a later view revived the historically authentic position that it
is a four note ornament starting on the upper note. Similarly a trill used to be viewed as
starting on the main note but a later view also revived the historically authentic position
that it starts on the upper note.
An exception in each case was admitted where the upper note had just been played in
which case the inverted mordent or trill started on the main note. In recent years the view
that the exception does not apply has gained momentum. The present writer, however,
does not support this view.
In Mozart the progression of views for trills has been the same as for Bach.
In Beethoven the progression of views for trills has tended to be the same as for Mozart
but there is an intermediate view that the trill started on the upper note in Beethoven’s
early period but tended to start on the main note in his middle and late periods.
In Chopin we know, from reports of lessons he gave and from his statement that he
followed C.P.E. Bach’s practice, that ornamentation and arpeggiated chords start on the
beat and that trills start on the upper note. When Chopin wants the trill to start on the
main note he notates the main note as a grace note immediately before the trilled note.
There do seem to be cases, however, where a Chopin trill sounds better when it is started
on the main note.
Chopin’s pupil Karl Mikuli wrote that in Chopin double-handed arpeggios always
proceed in one motion from left to right even if there is a break in the arpeggio sign
between the two staves.