First concept: Speaker settings cannot change the mix of the music; so the lead/background balance on the original audio file is not changed. Test one would be to plug in some headphones as a comparison. This would remove the variables of speaker performance and placement, but would leave in any software-induced effects.
You also need to do the regular troubleshooting checks to see that both speakers are working, and at comparable volumes.
What could be changed is: frequency response, stereo image, and volume.
Have you recently moved your speakers to a different location? Walls, desks and other surfaces will emphasize different frequencies. Moving a speaked against a will will increase bass output typically 3 dB, while putting it into a corner can make 6 dB of difference.
Equalization as you have already investigated can emphasize a range of frequencies over others. While this won't 'separate' lead and background, if you have a 'scoop' out of the midrange, the critical vocal frequencies will be less audible.
Stereo image will be my #1 suspect: if you collapse a L-R stereo field to mono, any material that appears in the L and R channels will be either accentuated or diminished. What determines this is whether the material common to both channels is in-phase or out of phase in one channel compared to another. Phase refers to the polarity of the waveform; whether the speaker is pushing air forward or pulling backwards at that instant. On conventional speakers you can change the phase simply by swapping the red and black speaker wires on the terminals on the back of the speaker (turn OFF the amplifier before doing this...). Self-powered speakers will vary in your ability to change phase.
So here goes: Since lead vocals are typically in the centre of the stereo image, they appear more or less equally in the L and R channels. If you put the L channel out of phase compared to the R, then the L speaker would be pushing while the R speaker was pulling, and the centre would tend to be cancelled out (+1 added to -1 equals 0) . This would be most apparent if the signal were summed to mono, or if you had the speakers positioned very close together. Perhaps your speaker layout is conspiring to deliver the L and R signal out of phase to each other in the critical vocal frequencies when they reach your ears?
Overall volume affects the amount of 'detail' you hear, because the human ear does not respond in a linear fashion to all frequencies.
Also: Check your Sound Preference pane to make sure the L R panning is centered. Some speakers have switches or controls to change EQ built into the speaker, or to change the balance of the sub-woofer.
Thanks
Trevor
CanadaRAM.com
