Where the shape comes from
Speech 言 with one stroke added across the mouth, marking the vibration, the tone of what is said rather than its words — sound heard as distinct from meaning spoken. It names music directly in 音乐 and sound, voice, in 声音, and sits above 心, the heart, in 意, intention, meaning, the tone of a feeling felt inwardly before it is ever put into words.
汉字 filed under 音
No published character on HSK Guide is filed under this radical yet. 汉字库.