Music’s potential for social communication is oft argued a possible cue to its evolutionary origins. However, empirical evidence for this capacity to induce or regulate social behaviors with music only consists only of indirect effects - for instance, that background music can reduce conflict or that collective music making increases trust and cooperation. Because these effects can be mediated by other musical effects, such as emotion induction, relaxation or semantic connotations, it remains unknown whether music can directly communicate (i.e. encode, and be decoded as) social cues. In this study, we show that spontaneous dyadic musical interactions can not only mediate, but directly communicate complex positive and negative social attitudes such as conciliation, disdain or insolence, and that such communication relies for a significant part on extra-linguistic cues linked to temporal and harmonic coordination. These results establish that more diverse and complex social behavior is possible with music than previously believed, which opens avenues for vastly more diversified views on music processing that the intra-personal, performer-to-listener view of musical expression that has dominated the recent literature.