Sampling is a standard practice in the production of hip-hop and rap recordings, and it is increasingly used in other music genres as well. It involves including a clip of another recording as a repeating element of the new recording. Audacity, a free, open-source sound editing application, makes sampling easier by offering a number of tools that help you capture your sample and work it smoothly into your production tracks.
Open the MP3 file you wish to sample in Audacity. Play the track by clicking the "Play" button, which is the one with the right-pointing green arrow. As the track plays, you see a line with a green arrow on top move across the waveform of the track.
Click the "Pause" button (the one with two vertical bars) when you come to the beginning of the portion you'd like to sample. Choose the "Selection" cursor by clicking the tool button with a single vertical line in the upper-left toolbar. Then click the cursor at the point on the waveform where the music has been paused. This puts a line at the beginning of your selection.
Continue the track playback by clicking "Pause" again. When you come to the end of the section you want to sample, pause the track. Move the selection cursor over your line at the beginning of the selection; the cursor turns into a pointing finger. Click and drag the selection line to the point where the song is now paused. Your selection is now highlighted in blue.
Preview the selection by clicking the "Stop" button (the one with the yellow square in the middle) and then clicking "Play" again. Now only your selection plays back. You can adjust the point at which your selection begins and ends by mousing over the lines at either end of the selection, then clicking and dragging them to new locations.
Remove the sample from the original track by dropping down the "Edit" menu and clicking "Split." Your selection now appears in a new track all by itself.
Move the sample to any point in your project by selecting the "Move" cursor from the upper-left tool box, clicking on the sample and dragging it to a new location.
Duplicate the sample to play it multiple times in your production by selecting the sample and clicking "Edit," "Duplicate." The sample is duplicated in a new track.
If you want to be able to align the beats in your sample to the beats in your production, select the sample and then click "Analyze," "Beat Finder." Audacity creates a new label track under the sample, with a flag at each beat in the clip.
Because of the nature of the recording process, some samples may not actually be in perfect concert pitch. It may be necessary to use Audacity's Change Pitch effect (found under the "Effects" menu) to raise or lower the sample's pitch slightly so it's in tune with the rest of your production track.