Serenity is similar to the ‘joy / love / hope’ group of emotions, except with less emphasis on the happy or uplifting components. Like joy, serenity is best expressed using stable musical material. Unlike joy, however, serenity also comes through best with a low energy level and a gradual rate of change.
The stability provides comfort and dependability, but the low energy level also adds a relaxed element. Rather than being important or demanding, a serene section of music needs to be unobtrusive. An emphasis on gradual change also works here – sudden change will be too jarring (although sometimes it makes sense to have a jarring transition out of a serene section!).
Sadness is similar to serenity in the stability and low energy, but moves towards a predominantly minor tonality. Consonance can also help, but will depend on the overall tonal language of the song. Sadness
can also be used to convey a message or feeling of despair. Despair can work with more dissonant tonalities.
The minor tonality sets the general negative mood of the music. In this case, the stability and low energy set the kind of negative mood – rather than being exiting or jarring, there is a calmness and quiet – almost tranquility. Negative tranquility very easily triggers feelings of loss, aftermath or reflection on past misdeeds.