Two of my best friends also played clarinet, and we would have duetting sessions at each other's houses while our parents visited, until our respective bedtimes.
The frequency of use of particular call-sites appears to be influenced more by the presence (vocalizations) of un-mated females on particular boundaries, than by the daily duetting of neighbouring pairs.
Mates must have coordinating duets in order to be a proper match for each other, which means lone singers are very uncommon in the duetting barbet species.
The pair bond is maintained by ritualised behaviours, including pair-distinct (female initiated) antiphonal duetting and reverse mounting during courtship and incubation.