Audacity has Effect->Plugins->Vocal Remover.
You may need to download the Nyquist plugin.
Vocal Remover requires a stereo track.
It works best with lossless files like
like WAV or AIFF, rather than MP3 or
other compressed formats. It only
removes vocals or other audio that is
panned to center (sounds equally loud
in left and right). Vocals are often
mixed this way. Inverting one channel
then panning both to center cancels
out any audio which was originally
center-panned, making it inaudible.
This can remove some parts of the
audio you may want to keep, such as
drums, which are also often mixed to
center. If the vocals and other
centered parts differ in pitch, this
can be solved by removing only
selected frequencies.
Vocal Remover thus has three choices
of removal method. 'Simple' inverts
the entire frequency spectrum of one
channel. This may remove too much
music if other parts of the audio are
centered as well as the vocals. In
that case, try the other choices. If
the vocals are at a different pitch
than the other audio (such as a high
female voice), try 'Remove frequency
band'. This only removes frequencies
between a lower and upper limit which
you can enter in the 'Frequency
band...' box. Experiment by entering
what sounds like the most significant
frequency range of the original
vocals. If the other choices remove
too much audio in a particular
frequency range (such as low drums or
bass), try 'Retain frequency band'.
This only removes frequencies outside
the limits entered, retaining the
others.
