The idea of a tonal centre in Chinese Music is similar to that in Western music where the music revolves around a certain "key". Just as in Western music, modulation occurs when the melody starts to move away from this tonal centre.
However, Western music has the harmonic structure as its basis while Chinese music emphasizes more on the linear melodic progression of the music. As a result, the approach and treatment to tonality differs somewhat.
Within Chinese music itself, tonality takes various different forms in the music of different eras and different societies.
Modal modulation (同宮系統的犯調)
One form of changing the tonal centre is to use different modes in the progression of the piece of music, for example, from the aeolian mode to the ionian mode. This type of modulation occurs frequently in many pieces of Chinese music and because it uses the same notes on the scale albeit with a different tonic, it does not give a big feeling of change.
This is unlike Western music where the harmonic structure is emphasized and the change for example, from A minor to C major changes the soundscape of the music quite significantly.
Tonal modulation (非同宮系統的犯調)
This type of modulation is the type of modulation that is most often found in Western music. The tonic is based on the same degree of the scale, and the key is changed, for example from B major to E major.
In Chinese music, tonal changes within a piece of music is often used as a mean of changing the mood of the music. Rather than using the harmonic structure to affect the music as in Western music, the Chinese uses melodic progressions and changes in the melodic structure to affect the mood of the music. Hence, besides the above forms of modulations, there are a few other types of tonal changes which is rarely found in Western music.
In the operatic music such as the Qin Qiang (秦腔) and Wan Wan Qiang (碗碗腔) of the North Western area, different scales are used for different types of emotions portrayed in the music. The Tian Yin (甜音) is a scale using the pentatonic scale gzhasd while the Ku Yin (苦音) emphasizes the lowered 7 and the raised 4 instead of 6 and 3 of the Tian Yin scale. As can be seen in the examples below, music utilizing the Tian Yin scale is usually for cheerful, comedic parts of the opera while music utilizing the Ku Yin is mainly used for the sadder moods.
This first excerpt uses the Tian Yin scale.
This next excerpt is sadder in mood and uses the Ku Yin.
These types of scales can also be found in music of other areas in China. Chuan Opera (川劇) from Sichuan area, Dianju (滇劇), Guizhou Wen Qin (貴州文琴) and Qian Ju (黔劇) from Guizhou uses similar scales in their music too.
Cantonese Opera (粵劇) from Guangdong has Yi Fan Xian 乙反線 with zgs tuning for the instruments emphasizing zjf giving a similar effect to the Ku Yin as well.
In Peking Opera (京劇), a variation of this tonal changes is used. They have the Zheng and Fan Diao (正反調) to effect changes in mood but this effect is not achieved through changing notes but rather changing the entire scale. For example, in the Er Huang scale (二黃) the instruments are tuned to zgs wwhile in the Fan Er Huang scale (反二黃), the instruments are tuned to 1 5 . As a result, one scale is a fourth lower than the other and the Er Huang scale is usually used for slower, more composed and peaceful music while the Fan Er Huang is used for sadder, bleak music.
These ways of using different scales (and as a result melodic notes) in the music to effect a change in the mood of the music is something rarely seen in Western music because the linear progression of the music is emphasized much more than the vertical harmonic aspect of the music seen so often in Western music.