What effect is created by the pounding at the gate? What dramatic effects are achieved by having the murder take place offstage?This is a...

I suppose you refer to the repeated knockings at the south
gate of Inverness, knockings that occur at the end of act 2 scene 2, which is the scene
of Duncan's murder. As Macbeth is afraid to go back to Duncan's chamber and stands
absolutely confused as well as terrified to see his hands stained with Duncan's blood,
the first knock is heard:

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..............................Whence is that
knocking?

How is 't with me, when every noise appals
me?

These
knockings continue in the following scene when the tipsy porter appears. He is supposed
to open the gate and allow Macduff and Lennox enter. These repeated knockings correspond
with shocking thrusts of guilt and fear in the mind of Macbeth. This is surely a
deliberate audio-effect that adds to the suspense of the
moment.

The murder of Duncan taking place offstage is a
masterly stroke by which Shakespeare opts for intricate psychological realism in place
of crude sensationalism of bloodshed. The severely fear-stricken mind of Macbeth and the
ironically antithetical  boldness of his accomplice, Lady Macbeth are thus revealed as
two contrary mirrors imaging the murder and its immediate repercussions in a wonderfully
theatrical manner. The physical act of killing would have failed to produce the desired
psychological complexities as shown in the scene.