I have used the audiokaraoke plugin to remove the voice of the song. It works well on some songs, but it only makes a little difference on the other songs. What can I do to improve it by using other plugins, or by combining audiokaraoke with other plugins? Thanks in advance.
There is no guaranteed way to remove a voice from a mix. You can try to use the equalizer and see if you can lower some frequency bands in the range of 800-2500 Hz, but that will most likely also affect the instruments.
To give a little explanation, if I ask: "the sum is 8 what where the addends?" there are multiple answers (e.g. 4+4, 2+3+3, 1+2+3+2, ...). For a mix we don't know the original tracks before mixing and not even the number of tracks.
The audiokaraoke plugin mostly relies that the voice is placed in the stereo center and looks at typical frequencies of the himan voice. If the voice has lots of effects applied, those will most likely remain in the result :/