Examples of these are rhythm syncopation, key tonality, and vocal harmonies. The most fundamental concept of Schenker's theory of tonality may be that of "tonal space". This is unacceptable in tonality; hence, tonal functions cannot be used. In music, modulation is the change from one tonality (tonic, or tonal center) to another. It is also harmonically unusual because of its ambiguous tonality. He occasionally uses the diatonic scale, with rapidly changing tonality. The sound here, while focused on a particular tonality, has ideas of chromaticism. More powerful techniques for improving tonality are referred to as tone mapping. However, the pentatonic scale has a unique character and is complete in terms of tonality. A second direction in the search for a new tonality was twelve-tone serialism. This differentiation between outer and inner voices was an outgrowth of both tonality and homophony. N'Ko uses diacritical marks to denote tonality and vowel length. "melodic tonality plus modulation is [Debussy's] modern tonality" . Human music may echo these phenomena using patterns, repetition and tonality. Analysis based on tonality and contrast are particular examples.