What's a good freeware or open source music editor software?

Yes, Audacity can handle that..

It uses the same vocal removal method as any other app (whether standalone or part of a program) but once a track has been mixed down to stereo the effect is limited.

Audacity:

http://audacity.sourceforge.net/

Lame if needed to encode to mp3:

http://lame.sourceforge.net/

How to install Lame:

http://audacity.sourceforge.net/help/faq?s=install...

Basic tutorials:

http://audacity.sourceforge.net/manual-1.2/tutoria...

http://www.recipester.org/Software/Audacity

Vocal removal method:

This is possible only for certain stereo tracks. When the vocals are exactly the same on both stereo channels, you can remove them by “subtracting” one channel from the other. This works for many studio recordings, where the vocal track is mixed exactly in the center. Be aware that bass and drums are usually panned to the center and can be removed or reduced also. Depending on how the track was mixed the vocal may only be reduced, not fully removed.

To do this in Audacity 1.2:

1. Import your stereo file into Audacity.

2. Open the track menu (click the arrow next to the track title), and choose “Split Stereo Track.”

3. Select the lower track (the right channel) by clicking it in the area around the mute/solo buttons.

4. Choose “Invert” from the Effects menu.

5. Using the track menus, change each track to “Mono.”

Press the Play button to hear the results. If you are lucky, the voice will be gone but most of the other instruments will be unaffected, just like a karaoke track. You can use the Export commands in the File menu to save the results.

Audacity 1.3.12:

Has a vocal remover built in. Just select the whole track then vocal remover from the effect menu.

I don't know if it has all the features you're looking for, but Audacity is kind of the standard free audio editor. http://audacity.sourceforge.net/

download NCH software suite it has all you should need also known as NCH toolbox