Open your preferred music production software, such as Logic or Pro Tools. Double-click the desktop icon or select the program from the "Start" menu in Windows, or "Applications" folder in Mac Operating System
Click "File" and select "Import." Select the bass line audio file from your library. The bass line audio will load automatically into your production interface. If you don't have individual files, import the entire track from which you want to sample.
Open "Multi-band Compressor." If you only have the master recording and no individual bass line files, you need to filter out the bass line from the rest of the audio. Increase the the level of the lowest frequency band in the multi-band compressor. This boosts the bass frequency. Reduce the level of all other frequency bands to cut the higher sounds, such as voice and guitar, to isolate the bass line. You can use the multi-band compressor to enhance the bass frequency of an individual bass file too, if you wish to apply a different tonal characteristic to the source file. However, this isn't necessary to get a good sample.
Open up "Sample Editor." To open it in Logic, click the "Sample Editor" tab at the bottom of the "Arrange Window". In Pro Tools, open up the sample editor by double-clicking the audio file. The sample editor presents the audio as a wave form graphic, the audio level is represented by peaks and dips.
Press play and listen to the bass line, follow the peaks and dips as the scroll along the screen. Pause the track at the point where you want the sample to begin. Make a note of the bar number where the first peak in the intended appears.
Select "Scissors" from the "Tools" menu. Click "View," select "Zoom" and then select "200 %" to enlarge the graphic. Click the scissor tool to the left of the sound wave where you want the sample to begin.
Hit "Play" and pause the track where you want the sample to end. Zoom in and click the scissor tool to the right of where you want the sample to finish.
Delete all audio from the left and right of the selected sample section.