To load the file, in the Attribute Manager, click the button that is next to the Filename text box. Use the dialog that opens to locate and open the sound file.
In the Attribute Manager, you will also find a setting called Probe. This defines how many samples will be used to calculate the amplitude — the greater the number of samples in this calculation, the more damped the sound will become. In other words, the sound gets quieter as you increase the Probe value.