refers to a good contrast between an important/strong/dynamic part and an unimportant/weak/static part.
is a monotonous life. means you should make the important part sound important and avoid a flat tone.
It's a bit difficult for me to explain what's , but I think it basically refers to some complex/dynamic/lively appearance.
is usually written in katakana (or sometimes hiragana). Etymologically, () referred to a low-pitched sound and () referred to a high-pitched sound. A kango equivalent of is , but is more often used figuratively.