Tutorial - Vocal Removal and Isolation
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. 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.
The current version of Audacity includes a Nyquist plug-in effect to automate the steps involved in Case 1, called Vocal Remover (for center-panned vocals), accessed from . It includes a Help screen and an option to retain a specified range of frequencies (thus removing everything outside that range). There are three choices of removal methods that can be used, for details see here.
Although two channels of output are produced the result will be mono because both channels will be identical and panned to center.
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 (where the mute/solo buttons are) then click on.
To delete one of the channels click theto left of the downward pointing arrow. If you accidentally delete the wrong channel, use to get it back. Finally, click the downward pointing arrow again and choose , 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.
- Peter 18Apr12: From the braindump notes that Gale provided (see the talk page) "Center pan isolation can't be done using the inversion, a.k.a. destructive interference, method of center pan removal; another method, spectral subtraction, is required, which is what the Extraboy and Kn0ck0ut plug-ins use". So it looks as though other s/w can perform the task , but not with center pan isolation.
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 this page 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 Removal to capture the noise profile of a song that has had vocals removed, then run Noise Removal with that profile on the original mix before vocals were removed.
- Make a copy of your original stereo track
- Select the whole track (click in the space its Track Control Panel)
- Copy the track with
- Create a new stereo track with
- Use to make a copy of the original track in the new stereo track
- Select the whole of the copied track (click in the space its Track Control Panel)
- Remove the vocals in the copy by using
- On a copy of the track remove the vocals as in Case 1 above using Audacity's Vocal Remover
- The copied track should remain selected, so use and click on the Get Noise Profile button
- Now select the original track (click in the space its Track Control Panel)
- Use OK button and click on the
- Delete the copied track (click in the at the top left of its Track Control Panel)
- Peter 18Apr12: This is what Andy Latham responded to the OP (Marco Diego): "Wow, I am really impressed. That's a much better method than anything I've ever heard before. It's still tricky to get rid of anything else in the center (this almost always includes the bass guitar and bass drum), but careful use of EQ can get you a pretty good result.", in this thread on the forum. From that I infer Andy meant that you could try filtering out some of the low frequencies. Is that a good guess?
It's still tricky to get rid of anything else in the center (this almost always includes the bass guitar and bass drum), but careful use ofcan sometimes get you a pretty good result.
- 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.
- Open Audacity and Import both the regular and instrumental tracks.
- Select one of the tracks and use the Time Shift tool to roughly align the two tracks.
- Zoom in really close and then zoom in more.
- 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.
- Select the instrumental track, and invert it using .
- Use Ctrl+A to select all of both tracks.
- Use .
You should now have one combined track that should have a more diminished amplitude where the vocals were kept and the instrumentation removed.
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 this page in the Audacity Wiki for details.