The ornamental design for a transducer, as shown and described.
FIG. 1 is a perspective view of a transducer showing my new design.
FIG. 2 is a front view of a transducer.
FIG. 3 is a rear view of a transducer.
FIG. 4 is a left side view of a transducer.
FIG. 5 is a right side view of a transducer.
FIG. 6 is a top view of a transducer; and,
FIG. 7 is a bottom view of a transducer. Any shading and cross-hatching are not features of the design but are utilized to illustrate the surface contours of the transducer design in the drawings.