Fantastic opera by Bizet. I believe you refer to the scene in Act 2 when Carmen sings and dances for Jose who has left his military post to be with Carmen. The bugle is calling him back.
While it is possible to simulate the effect of getting closer and closer by playing in the orchestra pit and starting to play softly and then progressively louder, in opera (and also in concert pieces calling for a similar effect) the player will literally be off stage in the wings and will play from a distance while walking closer and closer to the stage where the singers are, creating a much more realistic effect. Many opera scores call for singers and/or musicians to sing or play off stage in the wings in addition to the orchestra in the orchestra pit and singers on stage.
While it is possible to simulate the effect of getting closer and closer by playing in the orchestra pit and starting to play softly and then progressively louder, in opera (and also in concert pieces calling for a similar effect) the player will literally be off stage in the wings and will play from a distance while walking closer and closer to the stage where the singers are, creating a much more realistic effect. Many opera scores call for singers and/or musicians to sing or play off stage in the wings in addition to the orchestra in the orchestra pit and singers on stage.