Musical Grace quietly slowing down with hesitation, stifling tremulous sound (12)

'musical grace' is the definition.
'pralltriller' can be an answer for 'grace' (thesaurus). I'm not sure about the 'musical' bit.

'quietly slowing down with hesitation stifling tremulous sound' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'slowing down with' becomes 'rall' (I can't explain this - if you can you should give a lot more credence to this answer).
'hesitation' becomes 'er' (sound used when hesitating).
'stifling' means one lot of letters goes inside another.
'tremulous sound' becomes 'trill' (I've seen this in another clue).
'rall'+'er'='raller'
'raller' placed around 'trill' is 'ralltriller'.
'p'+'ralltriller'='PRALLTRILLER'

Can you help me to learn more?