Tone down the vocal support, being despondent (9)
I believe the answer is:
cheerless
'being despondent' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cheerless that I've seen before include "Miserable" , "not hip?" , "Bleak" , "Gloomy, depressing" , "Dreary" .)