Minimize all applications, such as web browsers and word processors.
Double-click the desktop icon to launch Soundbooth. Depending on your preference settings, Soundbooth with either launch a blank session or the last-saved session will open automatically. In the case of the latter, click file and select "Open."
Click on the relevant recording session in the drop-down menu. Once open, you will be able to import music from your library into the recording session interface.
Write down the tempo of the recording. The tempo appears in a small box on the bottom of the screen. It is typically a three-digit or two-digit figure, followed by the abbreviation "BPM," which stands for "beats per minute."
Click the "Restore Down" button in the top-right of the Soundbooth interface. This is the button between "Minimize" and "Close," it shrinks the window so you can see the desktop.
Open your music-file folder and drag the song to be used into the Soundbooth "Edit" window.
Click on the imported song audio file in the editor window. This highlights it and assigns subsequent commands to that audio only, rather than all audio.
Click "Processes" and select "Change Pitch and Timing." It is very unlikely that the audio you have imported and the recording you have made are at the same tempo. Two pieces of audio played back together at different tempos will sound messy and out-of-time. By adjusting the tempo of the imported song, you can "beat-match" the two audio files so they work together. This is a similar process to how a DJ mixes one song into the next.
Drag the song audio file to the right to "stretch" it. Watch the figure in the dialog box that appears. This figure tells you the new tempo of the song as you are stretching it. Stop dragging the audio file when the figure in the box matches the tempo of the original recording. If the start tempo of the imported song is greater than that of the recording, drag the audio to the right to decrease the tempo.