One of the most frequent problems I have encountered with students in my teaching, examining, and adjudicating is their approach to cross-rhythms. Yet, a lack of confidence—even fear—can easily be overcome by informed analysis and practical application.
I therefore encourage students to accompany me through the following stages. My examples come exclusively from the Chopin Nocturnes. These include a wide range of cross-rhythms, and provide a benchmark for other composers.
Before proceeding with the examples, let me share with you my views on how to coordinate both hands in order to successfully articulate opposing rhythms.
As an expressive art, I believe Music must not be approached mechanically. Rubato is always present and, to a greater or lesser degree, governs interpretation. With this in mind, I am convinced the only way to approach a cross-rhythm is to be aware that one rhythmic group has to be played evenly, with the opposing group subservient in an accommodating, though uneven, manner. The even group, in effect, acts as a guide to the uneven group.
The question now is: Which hand is the even one and which is the uneven? At the risk of sounding evasive, I have discovered there is no hard and fast rule. The performer must decide, within a passage's context, what best serves the musical flow.
Starting with the most basic of cross-rhythms, three notes against two, it is not difficult to see that the second note of the duplet figures comes between the second and third notes of the triplet figures. Referring to what I said in the previous paragraph, here the right hand would seem to be rhythmically the "straighter" of the two hands, with the left hand "fitting in" (see Excerpt 1).
Yet, conversely, during the climactic moment in measure seventeen of the same Nocturne, the music seems to flow better and more spaciously if the accompanying left hand is played "straighter" (see Excerpt 2).
From three-against-two, the challenge increases with more complex examples. In the Chopin Nocturne in E minor, Op. 72, No. 1, an examination favorite, there is a section where a sequence of four-against-three, eight-against-three, and ten-against-thee cross-rhythms follow in quick succession. Frequently, I hear these bars played in a panic-stricken, uncoordinated manner that must frustrate both performer and listener alike.
So how can this be overcome? The first task is to clarify the mathematical note positioning between the two opposing rhythms (see Excerpt 3).
Let me quickly point out that there is room for small adjustments to be made in the note positioning, so as to accommodate some variation of rubato by different interpreters.
Once firm decisions have been made about the note positioning, it is time to implement them. I would recommend, that in order to ensure confidence and consistency, it may be helpful to divide each passage into subdivisions and practice each subdivision separately.
To illustrate, I have selected measures thirty-one to thirty-six of the E-Minor Nocturne. In drawing an arc to cover each sub-division I have added an accent at the precise note where the hands interchange (see Excerpt 4). This produces a "bouncing" effect for what follows. Having played the accented note, the performer should stop, play the section slowly at first, and then gradually build up the speed to the required tempo. This should be repeated several times, before proceeding a stage further, adding the next subdivision to the first subdivision. The stages of this process should continue until the whole passage is completed. The accents can then be deleted.
Finally, having achieved confidence in executing cross-rhythms at all levels of complexity, the time has come to explore how a particular passage may be more creatively and freely articulated beyond what is indicated in the written score. To illustrate this I have selected an excerpt from the Nocturne in F-Sharp Major, Op. 15, No. 2.
Mathematically, this is an exact division of forty-against-four and is, strictly speaking, not a cross-rhythm. However, to reconcile this musically is not so straightforward.
The first eighteen notes in the forty-note block are shaped as triplets and the remaining twenty-two act as a resolution factor. To capture the decorative, yet improvised character of the music and avoid a metronomic and jerky result, small adjustments as to where the left hand fits in need to be made. In effect, a cross-rhythm is created for artistic purposes.
Excerpt 5 shows the exact mathematical division, and Excerpt 6 demonstrates a suggested musical solution. Let me quickly emphasize, however, that the latter is subjective. Others may prefer their own creative solution. Such is the joy of interpretation
Cross-rhythms frequently receive insufficient, unfocused attention. As a result, some pianists tend to bluster or fake their way through. However, if a player is to achieve a high degree of pianism, an informed approach is required.