Band is obliged to stand, welcoming soprano (4)
I believe the answer is:
sash
'band' is the definition.
(sash is a kind of band)
'is obliged to stand welcoming soprano' is the wordplay.
'is obliged' becomes 'has'.
'to stand' says the letters should be written backwards (I've seen 'standing' mean this).
'welcoming' indicates putting letters inside (in sense of 'inviting in').
'soprano' becomes 's' (musical abbreviation).
'has' written backwards gives 'sah'.
'sah' placed around 's' is 'SASH'.
(Other definitions for sash that I've seen before include "Cummerbund" , "Decorative band" , "Strip of cloth - type of window" , "Piece of cloth round waist or shoulder" , "Strip of cloth worn round the waist" .)