I am trying to turn out video that meets the ITU R BS1770 standard so I downloaded a speech sample that has a loudness range LKFS -24 (the gold standard) this works out to -20 db and true peaks should be -12. To avoid microphone variences, preamp distortion and so on I loaded a -20 db1kHz to my computer with the speech sample. I played it thru my Sony PCM D-50 output (
Output impedance: 220 ohms;Output level: 1.7V; Load impedance 22k ohms
Total Harmonic Distortion (Line Input to Line Output) 0.01% or below (1kHz, 22kHz LPF)
S/N Ratio 93dB or greater (1kHz IHF-A) when set to 24-bit) and into the Sescom to the GH2.
IT's Hot: even setting the sony to record the -20db tone exactly at -20db by the time it got to the GH2 it was -12db NO MATTER WHAT MIC LEVEL WAS SET. I tried all mic settings and apparently when you plug in a mic they are disabled.
I looked at the wave on both the Sony and GH2 (after removing 8db from the GH2) I could see very little evidence of the ACG. I was able to get a floor noise out of GH2 to -72db very acceptable, other than that there was no evidence of a lack in dynamic range, the gh2 showed only two spots of clipping making me believe it's not pumping up the gain, rather limiting the peaks.
The quality was very good but: if your feeding it with a recorder or preamp I suggest lowering the db 8-10 more than normal;since I am recording into the Sony at 24bit I can take the hit but nice to know the GH2 audio is really pretty good.
Why both? Plural eyes has failed me using just the built in mic (which the forementioned mic level is for I guess), I've been too far away from my subject.
On the GH13 the -20 db tone showed up as -8db. So turn down those pre amps and recorder outputs folks.
Please comment.

It's been recommended using the Rode Videomic Pro to set to -20, on the GH2, and that's what I do in a party environment. For interviews I run mic normally. Seems to work well.

Good point Jeff. I have been using the -20db setting on the Rode Mic Pro as well. For other mics, it is a good idea to use an attenuator (pad) on the input. Without one it's very easy to clip the audio. I don't why the preamp is so hot on the GH2 but it is.

My tests show that -20 is still to hot, also does anyone notice that the mic level doen't work when you plug a mic in?

Long story short, I have gotten very mixed results, sometimes it's been great, sometimes it's so hot it's worthless.

I've just received my new used HV30. I'm running it for audio from now on, that way there is no guessing. I can't count on good audio from the GH2, and am tired of messing with it.

I should say specifically the audio is very good in normal interviews, etc., but in a loud enviroment, it's too unpredictable.

So far so good using good mics, a good preamp and passing thru a good recorder with a great limiter

Good to know Roy. I run four cams (now five with the HV30 for audio) and adding preamps, etc is too complicated for me. I need to remove camera from tripod in an instant, if needed and I just don't want extraneous stuff to add or remove. It's already too much for me, as I work alone much of the time. (Sound crazy enough?) I do have an assitant now, but I don't want to have to count on having her. If I can't do it alone, then my setup is wrong somehow.

I'm currently running my audio through an H4N (various mics for various situations), I guess if I wanted too I could have it output to the GH2 then I have two copies.

I'm using an Olympus voice recorder with a shotgun, but it will not have the quality of your Zoom, for sure. I'll be putting it on a stand with a shotgun microphone as a back up.

Zoom H4n is what I use, as well. Amazing quality.