This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
A common reason for wanting to do this is to have a disc that can be sung
along with, either for personal practice or for karaoke. There isn't a
perfect method for doing this, but it's possible to get close with some CDs.
Music is generally recorded in independent tracks and then mixed into a
balanced whole. The recording studio can create masters with or without
the vocals, which is where a "clean" karaoke source comes from. The music
is usually recorded in stereo, and the vocals in mono (the singer has one
microphone). The mixed result has slightly different signals on the left
and right channels for the music, but the same signal on both channels
for the vocals. By removing all signal components that are equal on the
left and right channels, the vocals can be removed with relatively little
distortion of the music. This is called "center channel elimination".
This doesn't always work out in practice. If the track in question doesn't
keep the vocals "centered", all bets are off. Many musicians apply effects
to the vocals to achieve a certain effect -- often, to make it sound like
they can sing better than they actually can. These effects aren't usually
"centered", so part of the voice remains.
Center channel elimination can be done with a good sound editor, such as
Cool Edit 2000 or GoldWave. The procedure to follow with Cool Edit is:
- Extract the CD track into a WAV file.
- Load the WAV file into Cool Edit.
- Create a new window with no WAV file in it (File->New...). Set the
settings at 44.1KHz 16-bit *mono*.
- Switch back to the original WAV file (with the "Window" menu).
- Select the entire left channel in the original WAV file. If you move
the mouse to the top of the WAV display area, the mouse cursor gets a
little 'L' next to it. Pick a spot near the middle of the screen,
left click, and drag all the way to the left edge. Then move the cursor
back to the middle, right click, and drag all the way to the right edge.
You should now have the entire left channel selected.
- Select "copy". Switch to the new WAV file, and select "paste". Switch
back to the original.
- Move the mouse cursor near the bottom of the WAV graphic until the mouse
pointer gets an 'R' next to it, and select the entire right channel the
way you did the left.
- Select "copy". Switch to the new WAV file. From the Edit menu, select
- Select "Overlap (Mix)", volume of 100, and check the "Invert" checkbox.
GoldWave now includes a "Reduce Vocals" feature. Simply extract the CD
track into a WAV file and select it from the Effects menu.
The result is a single track with the center channel removed. Hit the
"play" button and see what it sounds like.
The converse operation -- extracting the vocals and deleting the music --
is not currently possible. (If you express the situation mathematically,
the problem is one of three variables in two equations. The software
needs a new feature that subtracts tracks and retains the other part.)