The looping features of Advanced Audio Editor (AudioSurgeon) can be used to 
create samples for a synthesizer or just to easily play back a section of your
song. You can position the Start and End points at the beginning and end of
the currently selected range (as illustrated below) by right clicking in the 
range and selecting Set Loop To Selected Range. If no loop points are set, 
the points appear at the beginning and end of the waveform. 

   

Clicking outside of the range will un-highlight the range, but the loop points
still show where it was originally positioned. 

Selecting Loop > Play Loop will play the portion of the waveform between the
markers. Loop > Play Loop with Attack will play the file from the beginning
and then repeat the loop, as it would in a sampler keyboard.

Typically, a selected range will pop at the loop point each time playback
cycles around, due to a level offset at the beginning and end of the loop. 
To remove this offset, use the Loop > Adjust Loop Start/End > Previous/Next 
Zero Crossing commands.

    A Zero Crossing is the point where the polarity of audio samples switches
    from negative to positive (or vice versa). These points are convenient 
    locations to make splices since the amplitude of sound at that point 
    is zero. 

This will locate the nearest point where the waveform crosses the zero 
amplitude mark. Once the start and end points are set to zero, the pop 
should disappear.

    Amplitude refers to the strength of the signal. In audio terms, this 
    is a measure of the volume of the waveform.

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