In typical recordings, the voice is usually recorded in the center of a monaural or stereo field. Most plug-ins are designed to analyze the center of those fields and reduce or eliminate the voice from the recording.
Most audio processing programs have integrated programs that specialize in audio removal. There are plug-ins that are also available as shareware or freeware programs. Third-party audio plug in programs are typically loaded to the main folder of the audio processing software and initialized from within the program.
Keep in mind that there are other instruments such as a bass guitar or kick drum that "share" the center of the monaural or stereo field. Reduction or removal of a vocal can also reduce the sound quality of those instruments. If the instruments are panned to the left or right of these fields, the vocal track should be removed with little effect on other instruments.
Plug-in examples include Audacity Vocal removal, DirectX Vocal Removal and YoGen Vocal Removal. Vocal removal plug-ins range from shareware and freeware to paid audio processing packages such as Adobe Audition and Wavelab software which cost in range between $149.00 to 795.00 dollars.