Hi Eric
I had the same trouble .I tried for 2 weeks, SM58 and AKG micros and different settings with results that made me uneasy.
My voice:100%
My singer voice:0%
The solution:
1-A fine setting of input signal.
2-Only 10% of noyse gate.
and... A US$8 mic from my daughter's karaoke.
Regards,Chico