Your success with isolating vocals from a song depends almost entirely on how the song was mixed, and will vary greatly. There is no perfect solution, though many times the artifacts that remain can be minimized within a mix. Generally, you'll have the best success with music where the vocals are panned to a specific location in the mix - usually dead center, but the tool can be used to isolate any position in the stereo field - without too much instrumentation spreading into this area. Bass sounds are usually mixed center as well, so you may need to to some additional EQ or Spectral removal of low frequencies after you complete the extraction step.
The tool you'll want to use in Audition is the Center Channel Extractor effect, located under the Effects > Stereo Imagery menu. Start with the Acapella preset, then change the Extract parameter to Custom for some additional control. Select the region you wish to isolate (it's often better to isolate passages separately as, for example, verses can be mixed very differently from a chorus) and begin playback with the effect open. Use the Power button to temporarily bypass the effect so you can note the differences.
Adjust the Phase Angle and Pan parameters to maximize the vocals while minimizing the instrumentation. Use the Frequency Range parameters to help reduce some of the low-end and high-end mix that is not associated with the vocals. The two vertical controls on the right allow you to adjust the levels of what's being isolated vs. everything else. (Flip-Flop these to make a Karaoke mix.) Under the Discrimination tab, the most important parameters will be the Crossover Bleed and Phase Discrimination controls. You can adjust the FFT parameters under the Advanced tab, though I wouldn't recommend it until you're comfortable with the tool. You don't necessarily need to know exactly what ever parameter does, but listen closely while you make adjustments and you'll begin to understand how each parameter affects the result.
dear i want only voice without background music?how can i do?can u tel me plzzzz
The instructions in the post above yours from Durin tells you exactly how to do it.
Awesome! Thanks for this. It worked great for me. I followed your instructions to the T and was able to remove most of the unwanted background music from my file. Getting into the Discrimination tab was the real key for me. When I adjusted and experimented with the parameters within that tab I found I was able to greatly reduce the unwanted bg music and enhance the vocals nicely. I used your technique as well as a little bit of the noise reduction tool where there was music, but no vocals as the speaker was taking a pause. Thanks!