Should i use Stereo expander (Wide field) on background music so vocal and music sound separate or is this really dumb question?
P.S - I dont know if this is important but voice is recorded in mono.While Background music is stereo.
It depends what you are trying to accomplish. Generally, you can accomplish the stereo expander's effect by using a bit of reverb. You'll want to also filter out any bass frequencies from that channel as well
Stereo Expanders are used all the time in lots of different contexts, but there are three things to watch out for when you do:
1: EQ. When the sound is stretched wide you can lose bass frequencies from the middle of the mix, or they can sound weird.
2: Wideners often use slight delays to the signal (panned hard left and right) which can cause phasing issues. Always check your mix in mono to make sure it still works.
3: Wideners can also use slight pitch shifting between left and right, which can result in a loss of musicality. Things like sound effects of explosions can be widened like crazy with no issues, but something like an orchestral symphony should be treated with some caution.
The basic answer is yes, use it, but look out for the above and tweak the settings to minimise any problems you can hear. I don't know if you're on Windows, but I have found the free SHEPPi Spatial Enhancer VST very useful for this kind of job.