For the Pressure Acoustics, Transient interface, you can in addition to the User Defined and 
Flow option select a predefined 
Gaussian pulse as a source 
Type for the 
Line Source, 
Line Source on Axis, 
Monopole Point Source, 
Point Sources (for 2D Components), and 
Circular Source (for 2D Axisymmetric Components) features. This type adds a source with a Gaussian time profile defined in terms of its amplitude 
A, its frequency bandwidth
 f0, and the pulse peak time 
tp. Using this source type results in solving a wave equation of the type:
 
    In 3D components (for Line Source), 2D axisymmetric components (for 
Line Source on Axis and 
Circular Source (for 2D Axisymmetric Components)), and 2D components (for 
Point Sources (for 2D Components)), all of which are effectively line sources, enter the following values or expressions: