One picture carries most of this word: something shaking in small, quick, repeated movements. Not one big shock — a fine that keeps going, like a candle flame that will not sit still. Put that into the sound of a person speaking, and you have the uses you meet most often.
The supplied source entry traces quaver to Middle English quaveren, a frequentative form of quaven, 'to tremble'. A frequentative names an action done again and again, which fits the modern picture: not one shake, but shaking that repeats.
這份資料裡的來源條目說 quaver 來自中古英語 quaveren，是 quaven（發抖）的反覆形式。反覆形式指的是「一做再做」的動作，正好對上今天的畫面：不是抖一下，而是一直抖。
Wiktionary entry supplied in this packet (source_ref kaikki:3f6f69a190036ae4:106985328:16772): 'From Middle English quaveren, frequentative form of quaven, cwavien (to tremble)'
From the picture
音樂：八分音符（英式說法）
這個用法和上面共用同一個字。可以把它想成一個短短的、一閃而過的音符，跟「細細地抖」放在一起記；不過這份資料並沒有說它在歷史上真的從「抖」長出來，所以只當成幫助記憶的聯想，不要當作字源。實際上要記的是它的制度面：長度是全音符的八分之一，而且這是英式名稱，美式叫 eighth note。
noun · C1
In British English, a musical note that lasts one eighth of the length of a semibreve (a whole note). It is written like a crotchet — a note head with a stem — plus one tail on the stem. American English calls the same note an eighth note.
八分音符
verb · C2
To shake with small, quick, repeated movements — used of things such as a flame, a light on water, or a held musical note. Learner dictionaries record only the voice meaning, so this wider use is one you are more likely to meet in older writing and in descriptive writing than in everyday speech.
微微顫動
verb · C1
If someone's voice quavers, it shakes a little while they are speaking or singing, usually because they are nervous, frightened, or upset. You can also say that the person quavers, especially when you are reporting the words they said.
聲音發顫
noun · C1
A slight shake in the sound of a person's voice, which you can hear when they are nervous, frightened, or feeling something strongly.
聲音裡的顫抖