Extracting vocals/voice, or any other sound for that matter from recordings, is not an exact science. You can still hear in the background a voice singing, this is often called 'sound by-product'. It is impossible to remove everything but with EVP you don't have too. It is possible to take sound a bit further to get better results but not by much plus it can become time consuming for little in return and you often take the extraction one step too far and start to remove sound you needed to keep.
Same recording but with vocals removed using software.
I have used the same procedure as the first movie at the top of this page.
There are clear differences between the sound files. What we have done here is to subtract the vocal band from the full sound file. What we now need to do is EXTRACT and SAVE the vocals, which is what you would do with a EVP file. As explained on a earlier chapter you can isolate any frequency using 'Riff Station' but the better results are found with a Digital Audio Workstation - DAW. I have put some thought into what the best DAW would be and come up with a FREE software Suite called 'Adobe Audition V3'. This software can be downloaded by following this LINK.
Here is the movie of importing the sound file into Adobe Audition 3.0 and applying EQ extraction and changing the frequency spectrum so we are left with just vocals or as much vocal we can.