The open-source, multi-track audio editor Audacity lets you copy, combine, cut and splice tracks as well as add filters and alter pitch and speed. Sometimes, however, tracks require more drastic changes; whether you're working on a remix or just want to bring your favorite song a little closer to the a capella realm, you can use Audacity to isolate vocals, eliminating or reducing the presence of background music. Unlike the program's key features, this process takes just a little more effort than a few clicks.
Open the song of your choice -- Audacity supports AIFF, FLAC, MP2, MP3, Ogg Vorbis and WAV formats -- and choose "Select All" from the drop-down Edit menu to select the entire track. From the Edit menu, select "Copy."
Hover over "Add New" and select "Stereo Track" from the drop-down Tracks menu to create a new track. This creates a new track with a left and right audio channel. From the Edit menu, click "Paste" to create a duplicate copy of the song in stereo.
Select the duplicate track and access the drop-down Effect menu. Choose the "Vocal Remover (for center-panned vocals)" option. Click "OK" on the dialog box that appears.
Choose "Noise Removal" from the Effect menu with the duplicate track still selected. Press the "Get Noise Profile" button on the window that appears. This causes Audacity to capture the track's noise profile.
Select the original track. Choose "Noise Removal" from the Effect menu once again, but this time press the "OK" button to apply the Noise Removal effect. This reduces or eliminates the audio presence of the backing music track.
For this technique to work successfully, you'll need to use a music track with center-panned vocals, as indicated by a light blue central line running through the track's waveform when displayed in Audacity. Modern music tracks are commonly center-panned.
The effect of the vocal isolation may vary per track. To heighten the effect, increase the “Noise Reduction (dB)” and “Sensitivity (dB)” sliders in the Noise Removal menu before applying the effect.