How would adjusting the bias on an op amp effect the signal?
The bias is typically set at half the supply voltage (in solutions without bipolar power supplies) because that puts it the farthest from clipping against either rail. You can adjust it up or down if you want, but the closer it gets to one rail the smaller the permissible signal variation in that direction.

Since most audio signals are symmetrical, moving it in either direction away from the midpoint reduces the maximum signal amplitude.