Tutorial - Vocal Removal and Isolation



This page describes techniques which, on some stereo tracks, may allow you to remove or isolate vocals (or other parts of a recording) from the rest. There is no universal, reliable way of doing this without having the original multi-track recordings. Different tracks will require different techniques to achieve maximum possible attenuation or isolation. This will depend on where the vocals are positioned in the stereo field, and on their frequency content compared to the rest of the audio.

Case 1: Vocal Removal with vocals in the middle and instruments spread around them
If the vocals are panned in the center of a stereo track the so-called "vocal removal" technique can sometimes be effective by removing what is common to both tracks (i.e. the vocals), leaving behind what is different (i.e. the instrumentals).

The underlying technique in Audacity is to split the stereo track into its left and right channels, make both mono, invert all (or a selected part) of one of them then play back the result. Note, this removes everything panned in the center, not just vocals, and returns a dual mono result (both channels have the same audio). In some music this could mean removing instrumental parts. Removal of the vocals can often be incomplete leaving artifacts behind; this is especially true where there are backing vocals or where reverb (echo) has been applied as this spreads sound sources and makes them very hard to extract from each other.

Vocal Reduction and Isolation
Audacity includes a Nyquist plug-in effect to automate the steps involved in Case 1, at Effect > Vocal Reduction and Isolation.... If you only wanted to automate Case 1 in the Vocal Reduction and Isolation effect, you would choose the option "Remove Center Classic (Mono)". As in Case 1 above, this removes the whole frequency spectrum of center-panned audio and returns a dual mono track.

However the default option for Vocal Reduction and Isolation "Remove Vocals" is to be preferred in most cases because this returns stereo output. As its name implies, this effect also offers "Isolate" options (which do return dual mono) which are an alternative to the isolation techniques given in Case 3 below.

Vocal Reduction and Isolation also lets you specify frequencies above which or below which audio is not removed or isolated. This can help cure the common problem where center-panned bass or Hi-hat is also removed when removing vocals.

Case 2: Vocal Removal with vocals in one channel and everything else in the other
If you have an unusual stereo track where the vocals are mixed hard into one channel and everything else hard into the other channel you can split the stereo track into left and right then delete the vocal channel. To isolate the vocals, rather than remove them, delete the other channel. To split a stereo track in Audacity, click on the downward pointing arrow at the top of the Track Control Panel then click on Split stereo track.

To delete one of the channels click the [X] to left of the downward pointing arrow. If you accidentally delete the wrong channel, use Edit > Undo to get it back. Finally, click the downward pointing arrow again and choose Mono, so that the track will play out of both speakers.

Case 3: Vocal Isolation
If you can make a two-channel track with center vocals removed (as in Case 1 above) it is tempting to think that those vocals can be isolated by inverting this track against the original track, so as to remove the non-vocals.

Vocals often cannot be isolated in this way. The result of the Audacity Vocal Removal effect is a mono mix of sound that was in the left and right channels but was not common in both. Mixing this back with the original track (either inverted or not inverted) will produce a stereo track that contains a new mix of the center panned vocal and the non-center sounds. Different techniques used by some third party plug-ins such as 'ExtraBoy' claim to be able to isolate vocals given suitable audio material (see Vocal Removal Plug-ins in the Audacity Wiki).

Using Audacity for vocal isolation
An Audacity user (Marco Diego) posted this technique on the Audacity Forum for using Audacity to attempt to isolate vocals; it will not work successfully in all cases.

It is sometimes possible to isolate vocals by using Audacity's Noise Reduction to capture the noise profile of a song that has had vocals removed, then run Noise Reduction with that profile on the original mix before vocals were removed.
 * 1) Make a copy of your original stereo track
 * 2) Select the whole track (click in empty space in its Track Control Panel for example where it says "Hz")
 * 3) Copy the track with Edit > Copy
 * 4) Create a new stereo track with Tracks > Add New > Stereo Track
 * 5) Use Edit > Paste to make a copy of the original track in the new stereo track
 * 6) Select the whole of the copied track (click in empty space in its Track Control Panel)
 * 7) Remove the vocals in the copy by using Effect > Vocal Remover (for center-panned vocals)...
 * 8) On a copy of the track remove the vocals as in Case 1 above using Audacity's Vocal Remover
 * 9) The copied track should remain selected, so use Effect > Noise Reduction... and click on the button
 * 10) Now select the original track (click in the space its Track Control Panel)
 * 11) Use Effect > Noise Reduction... and click on the button
 * 12) Delete the copied track (click in the [X] at the top left of its Track Control Panel)

The following may let you remove drums which are not centered but keep the vocals:
 * Use the steps above to create a track with vocal isolation.
 * Then import the original song into Audacity again and try this Nyquist plug-in elliptice.ny to move the bass frequencies to center.
 * Then remove the drums from the center by inversion.
 * Finally mix the vocals back in.

Using an instrumental track to isolate the vocals
In order for this to work you will need to have a studio version of the instrumental track in which the instrumental part is identical to the full track. Many studios release the instrumental tracks (with and without backup vocals) for use with things like karaoke. There are places online where you can buy these tracks (Karaoke-Version.com for example and some records even have them on the B side). MP3 encoding of one or both versions will create small differences that will make this technique less effective.

As opposed to the final mono track you get from removing vocals, this method will leave you with a full stereo track. As such, it becomes more important to try and match the quality of both tracks and align them before you isolate the vocals. You should now have one combined track that should have a more diminished amplitude where the vocals were kept and the instrumentation removed.
 * 1) Open Audacity and Import both the regular and instrumental tracks.
 * 2) Select one of the tracks and use the Time Shift tool to roughly align the two tracks.
 * 3) Zoom in really close and then zoom in more.
 * 4) Exact alignment is critical. Pick a peak or trough in the left channel of one track and match it precisely with the left channel of the other track. If the alignment isn’t right the process won’t work.
 * 5) Select the instrumental track, and invert it using Effect > Invert.
 * 6) Use to select all of both tracks.
 * 7) Use Tracks > Mix and Render.

Third-party plug-ins
As well as the above methods supported by Audacity itself there are various third-party plug-ins that can be used to try and remove or isolate vocals.

Please see Vocal Removal Plug-ins in the Audacity Wiki for details.

Gale commented in an email: "Another issue is how far can we go mentioning third-party plug-ins in the Manual, especially without verifying how effective they may be?"