Audio: leap (0:08)
leap plays steps and leaps in the key of A natural minor on a euphonium. The leap figure shows the score:
A leap or skip is a movement from one note to another in a scale which is greater than a step.
A leap is motion by three semitones or more in a mode or in the melodic minor scale. In the harmonic minor scale there is one leap of more than three semitones. In a chromatic scale, a leap is motion by two semitones or more.
A leap is a discontinuity. It has more impact on a listener than a step. To explain why we have to step, or leap, if you will, into the world of perception.
The Implication-Realisation model of melodic expectation (I-R model) really should have a catchier title. What it does is try to answer a difficult question: how does a listener perceive melody? Among the many interesting findings of research using the model is that a listener has different expectations from small leaps and big leaps, a small leap being classed as less than a tritone, five semitones or fewer.
The research found that there is considerable flexibility in the motion of a small leap. For example, the melody C-E in the key of C is a small leap of a third. This could lead to C-E-D, which is a step turn following the leap. It could also lead to C-E-F, which is a step in the same direction as the leap. It could also lead to C-E-G, which is two small leaps in succession. All these mixtures of steps and small leaps sound pleasing to a listener.
By contrast, a large leap changes the expectation of a listener. A large leap is expected to be followed by either a small step in the opposite direction or by lateral motion. For example, the melody progression C-G in the key of C is a large leap of a fifth. It is expected to become either C-G-F, a step turn down, or C-G-G, lateral motion. The same is true for a large leap downwards, G-C is expected to become G-C-D or G-C-C.
The model provides simple and useful guidelines for writing melodic motion: