Audacity is sound-editing software available free of cost online. The program can be easily downloaded onto your computer and is a useful tool to edit audio clips. Overlapping two audio clips is a relatively simple task using Audacity. When two or more audio clips are overlapped and exported as a single audio clip, the sounds from both clips are played simultaneously.
Launch Audacity and open one of the files you wish to overlap by clicking the "File" menu and clicking "Open."
Import the second audio file by clicking the "Project" menu and selecting "Import Audio." Select the second file. A new audio track will be created in the window.
Select the "Time Shift Tool." This tool is located in the left-top corner of the screen in the second row and the middle column of the six editing tool buttons.
Click and drag the tracks horizontally to adjust the positions of the audio clip relative to one another.
Click the "Play" button at the top of the screen to hear what the overlapped audio sounds like, and adjust the positions of the audio clips accordingly.
Export the overlapped audio clip by clicking the "File" menu and clicking "Export as WAV." A single WAV file will be exported.
The overlapped audio file can be also exported in the MP3 format by selecting “Export as MP3” under the “File” menu. Also, more than two tracks can be overlapped by repeating steps 2 through 5.