Double-click the desktop icon to launch your preferred digital audio workstation, such as Pro Tools or Cubase.
Open the "File" menu and click "Open." Select the session containing the beats to which you want to sync the audio. If your digital audio workstation automatically opens the last saved session and this isn't the one you need, quit that session.
Open the "File" menu again and select "Import." Browse your digital audio workstation file folders for the audio that you want to use. Once you find them, click on the file icon. This loads the vocals into the session interface, typically as "Audio 1." Any vocal that is unnacompanied is acapella, the term is derived from the Italian phrase "A capella," meaning "in the way of the chapel." Since you're extracting a vocal from the instrumental, it automatically becomes acapella, regardless of its previous context.
Double-click the file name "Audio 1" and rename it "Acapella."
Click on the vocal audio. This highlights it and assigns subsequent edits to just the vocal, not the entire mix.
Click "S" on the "Acapella" channel strip. This solos it, muting any beats you already have in the session.
Hit "Play" then right-click on the tempo bar. Select "Auto Detect." This function analyzes the energy patterns of the wave form to determine the tempo. Note the tempo it gives you.
Click "S" on the "Acapella" channel strip to unsolo it, then solo the beat and detect the tempo of that track. You now know by how much you need to edit the acapella track to match the beat.
Click on "Acapella" to highlight it.
Stretch the acapella audio. The method for doing so varies slightly according to which program you use. For example, in Cubase right-click the sound wave, click "Process" and select "Time Stretch." This opens a time-stretch interface. Enter the desired beats per minute into the box marked "BPM." In Fruity Loops, right-click and select "Elastic Tonal," then adjust the time knob to match the tempo of the acapella with the tempo of the beat. Digital audio workstations typically use resampling technology, so the pitch doesn't change when you alter the tempo.
Click "Save."