adjective

not showing any emotion; unemotional.

her voice was flat and emotionless

unemotional,unfeeling,dispassionate,passionless,unexpressive,cool,cold,cold-blooded,impassive,reserved,controlled,restrained,self-controlled,calm,and collected,indifferent,detached,remote,aloof,toneless,flat,dead,expressionless,bland,blank,wooden,stony,deadpan,hollow,vacant,undemonstrative,imperturbable,frigid,phlegmatic,glacial