I got my SM58 today, plugged it into my E-MU 0404 USB - set the microphone gain to +65db and shouting into the microphone barely registers in the -18dB LED.
Covering the microphone with my hand and speaking loudly into into it makes it jump to -12 or even -6dB but the "SL" light comes on.
Here is an example of a normalized recording of me speaking around 3cm away from the microphone: http://hackeron.dyndns.org/sm58_0404usb.wav
Normalization pushed volume +30dB even though I have +65dB set on the 0404USB and the background noise is unbearable. What the hell!?