I just got my new HV20 and DM-50 external mic, and I decided to go through a series of tests to see what sounds the best. I fiddled with different volume levels and with attenuate on and off.

The first series is of a silent room with different settings. The second series is the same setup, but with me speaking at about 6 feet away to see how recorded voices sound. All volume levels are straight out of the camera at 0.0db in vegas (except for one which I noted. I raised the volume to match the volume level before it.)

Overall, at least under typical conditions, I don't find the attenuate feature very useful. Volume levels are super quiet, and raising the volume as I did just reveals the strange hum, which sounds worse than the motor noise. Personally I like the -12db setting with attenuate off from the DM-50.

I've also thrown in a test at the end using the internal mic. The DM-50 might not be perfect, but it's a serious step up.