Tutorial - Vocal Removal and Isolation

Peter 16Apr12: Initial draft created from a modified version of the Wiki tutorial.
ToDo-2 ready for editorial reviewv and merciless editing.

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: Vocals in the middle, instruments spread round them

If the vocals are panned in the centre of a stereo track (fairly common in "pop" music tracks), the so-called "vocal removal" technique can sometimes be effective. This removes what is common to both tracks (i.e. the vocals), leaving behind what is different (i.e. the instrumentals).

To try this technique in Audacity, split the stereo track into its left and right channels, make both mono, invert all (or a selected part) of one of them, and play back the result. See this page of the Audacity FAQ for step-by-step instructions on this technique, or a YouTube video tutorial covering the same process.

Note this removes everything panned in the centre, not just vocals. In pop music this can mean removing the bass and rhythm parts. Removal of the vocals is normally incomplete and will leave artifacts behind, especially where reverberation (echo) is used, and where there are backing vocals. Sometimes certain minor strands of the instrumentals are exposed which are completely covered in the uninverted mix. This technique works particularly poorly with tracks where a lot of stereo reverberation has been applied, as this spreads each sound source, and makes them very hard to extract from each other.

Vocal Remover (for center-panned vocals)

In the current version of Audacity a new Nyquist plug-in effect has been added to automate the steps involved in Case 1; for fuller details see Vocal Remover.

It is accessed from Effect > Vocal Remover (for center-panned vocals).... It includes a Help screen and an option to retain a specified range of frequencies (so removing everything outside that range); there are three choices of removal methods that can be used; for details see here.

Note that although two channels of output are produced the result will be mono because both channels will be identical and panned to centre.

To install this plug-in, place "centerpanremover.ny" in the Plug-Ins folder inside the Audacity installation folder. On Windows computers, this is usually under C:\Program_Files\Audacity. After restarting Audacity, select the track or audio you wish to remove the center-panned elements from and click Effect > Vocal Remover (for center-panned vocals)...; it will be found underneath the divider in the Effect Menu.

Peter 16Apr12: ToDo-2 I don't think the above note is needed. Surely the Vocal Remover effect is automatically installed with v2.x - or am I wrong?

Case 2: Vocals in one channel, 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 simply split the stereo track into left and right and 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 (where the mute/solo buttons are ) then 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 be isolated by inverting this track against the original track, so as to remove the non-vocals?

Unfortunately vocals 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 with suitable audio material (see below).

Plug-ins

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

Windows Plug-ins

Two Windows VST plug-ins are known of that can be used in Audacity for vocal removal and isolation.

• kn0ck0ut (free) can sometimes remove vocals where they are not centre-panned but rather different in frequency make-up compared to the non-vocal parts of the track. It works on two mono tracks (split from a stereo track and made mono as above) by extracting the right channel frequencies from the left hand frequencies, leaving the "result" in the former left channel. Alternatively, if your vocals are centre-panned, this plug-in can often make a good job of isolating them from everything else.

• Voicetrap is a commercial plug-in featuring centre channel removal by frequency-based and cepstral methods (that is, not a simple subtraction of one channel from the other). It has an advantage over kn0ck0ut of providing stereo output for the "vocals removed" track, as well as offering isolation of centre-panned content. There is a demo version with a "mild" vocal removal setting (but no isolation ability) that works in Audacity.

To try either of these VST plug-ins in Audacity, place the unzipped .dll file from the plug-in's zip folder, and the unzipped vst-bridge.dll from the Audacity VST Enabler into Audacity's Plug-Ins folder. The Plug-Ins folder will be in the folder where you installed Audacity, usually C:\Program_Files\Audacity. On restarting Audacity, the new plug-in will appear in the Effect Menu underneath the divider. Should vst-bridge.dll not work, try the previous VST Enabler for Windows (place the already unzipped VST_Enabler.dll in Audacity's Plug-Ins folder along with the plug-in's own .dll, then exit and restart Audacity). Note that VST plug-ins in Audacity only have a generic tabular interface due to licensing restrictions imposed by Steinberg.

If you use the current version of Audacity, you do not need to add the VST Enabler to your computer to enable VST plug-ins. On first launch, Audacity should detect VST plug-ins in the Audacity installation folder. Also, Audacity will display the full interface for VST plug-ins that have a graphical interface. You can add further VST plug-ins later by checking the "Rescan" option in the Effects Preferences, then restarting Audacity.

There is also an additional commercial VST plug-in called ExtraBoy which offers useful functionality for those interested in vocal removal or modification of the different components of an audio track. There are two versions of this plug-in, but unfortunately neither work properly with the currently limited VST support that Audacity can offer. It seems that the processed audio is always completely silenced irresepective of the plug-in settings used. Both versions of ExtraBoy do function with other audio editors which offer full VST support, so you could always export a track from your Audacity Project as a WAV or AIFF file and process it in Extraboy in another editor.

The "lite" version of ExtraBoy is quite similar to VoiceTrap but offers some vocal removal ability on all tracks (not just on centre-panned vocals). It has two "vocal removal" algorithms (1) on the basis of the vocals' frequency characteristics, and (2) on the basis of their spread in the stereo spectrum. The two algorithms can be combined to obtain the best possible removal in a particular case, and full stereo information is preserved in the processed track. A "vocal isolation" algorithm is also provided.

The 14 day full-featured "demo" version claims to be capable of isolating, removing, suppressing or enhancing any component of a stereo track, based on its identified frequency and spatial "signature". Naturally the author points out that the exact results are subject to the particular characteristics of each track. Multiple components of a track can be processed simultaneously (for example, to isolate piano and vocal, or enhance piano and bass).

OS X Plug-ins

On OS X you can try the voxReducer Audio Units plug-in (14 day free evaluation) in Audacity, as long as you use the current version of Audacity. This requires OS X 10.4 or higher, although a legacy 1.3.3 version for OS X 10.3 is still available.

VoxReducer is similar to the Nyquist Center Pan Remover in that it aims to reduce the strength of centre-panned vocals, but differs in having a phase offset adjustment and a slider for adjusting the intensity of the vocal reduction.

Try putting the voxReducer.component in either of these two locations:

/Library/Audio/Plug-ins/LADSPA or

~/Library/Audio/Plug-ins/LADSPA

or (as suggested by the program documentation):

/Library/Audio/Plug-ins/Components or

~/Library/Audio/Plug-ins/Components

brainworx makes a vst plugin bx_solo that lets you solo mid and side channels. it also has a mono-izing knob and the ability to solo left or right channels. its also an AU and RTAS plugin and they're free.