I've been approached a few times by folk who want to remove vocals from a particular track for various reasons. Whilst this short guide will assist you to kill the vocals in songs - it is by no means guaranteed to work as it relies heavily on the way the song was recorded in the first place.
Understanding the basics of sound recording is key to understanding how this works.
Firstly - In a stereo image vocals are usually recorded and placed in the centre of the field. Most instrumentation is recorded and placed in different parts of the field in oder to maximise the stereo effect. The normal exception to this rule is the bass drum and often times bass guitar which are also normally sited in the centre of the stereo image. Almost always there will be an effect of some type on the vocal such as echo or reverb and I'll return to these effects later.
Now to understand the technicalities. A stereo image has a left and right channel. Audio that appears to eminate from the centre of those channels is equally divided between left and right. That placement can be eliminated completely by reversing the phase of ONE of the tracks (Left or Right). One effectively cancels out the other when the phase is reversed on either the left or right channel.
So, import your stereo song and for the purposes of Vegas users do the following.
Create TWO audio tracks and drag the media into track 1 on your timeline. You should see the left and right elements of the media in the track. Now drag it in again on track 2, ensuring they both start at exactly the same point. On the top track (1), right click the media and go down to 'Channels' and select 'Left Only'. On the lower track (2), do the same but this time select 'Right Only'.
Play the song - it'll sound perfectly correct at this point. All you've done so far is seperate left and right channels into two tracks that you can manipulate individually.
Now right click the lower track (2) media, and go down the drop menu to 'Switches' and select 'Invert Phase'.
Now play the track - everything in mono has gone. You'll almost certainly find the song has gone 'thin' sounding and you'll most likely hear some vocal spill. This spill is usually generated by the effects mentioned earlier. Sound engineers love to create stereo soundscapes and moving echo or reverb around is one trick they employ to achieve that. Sadly, there is not a great deal you can do to eliminate that spill, but hopefully it will be far enough back to be masked by the rest of the instrumentation.
As for the 'thin' sound you're left with - play with the graphic eq settings in the track FX. You may be able to boost the lower frequencies enough to lessen the loss and leave you with a reasonable sound.
PLEASE NOTE - This guide cannot be guaranteed to work as it relies heavily on the way the song was first recorded. As and example I have just imported a whole E.L.O. album and played with it track by track - around half of the songs are perfectly useable the rest have an excess of vocal trickery that renders this technique useless. The best advice is to play with as many songs as you can until you find one that works best.
Using the above and playing more with the inbuilt effects supplied in Vegas may even give you better results - Give it a try!