GH2 sound

Posted on 5 November 2012

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Sound is being tested, there is a seperate thread on Personal View. It’s also part of the new Driftwood Sedna patches as of 15/3/12.

  • The default bitrate of sound recording is 192kbps, which already is great. You can go up to 448kbps but it will make your files not playable in camera. 192kbps should be good for almost any use.
  • The real power lies in the microphone settings ->; AGC (Automatic Gain Control) Settings. You can set four AGC levels, which you can choose in the Motion Picture ->; Mic Level Adj. menu. For each of these AGC levels, you can set a value. These values influence the mic preamp, the digital amplification and the compressor/limiter. There is a lot of testing going on, as it seems like responses are not very logical. More to come.
    • To turn of the automation as far as possible: use 0x00 as the first bits. Original value for AGC 3 is 01: gain value + 256. The other AGC levels do are not above 255, so no automation.
    • The last two bits are for the (digital?) gain. It is said to reset around 112, for dynamics it would be best to stay between 118 and 255. Original values are:
      • AGC3: 266 (0x010A)
      • AGC2: 10 (0x000A)
      • AGC1: 22 (0x0016)
      • AGC0: 34 (0x0022)
  • Of course, if you set your AGC to sort-of manually control your recording, you will want to use your volume indicators. They have a scale of 8 leds (indicators) for each channel (total: 16 indicators), of which the first six are yellow and the upper two are red. You can set the values for each of these indicators. Also here testing is needed.

Testing input levels

The patch levels are:

  • AGC0 (mic level 1): 0 (don’t know the ref in dBu)
  • AGC1 (mic level 2): +13 dB
  • AGC2 (mic level 3): +21 dB
  • AGC3 (mic level 4): +37 dB

The indicator thresholds are:

  • indicator 5: -18 dBFs
  • indicator 6: -12 dBFs
  • indicator 7:   -6 dBFs
  • indicator 8:   -3 dBFs

I have tested the patch with my SoundDevices 302 mixer on the 2,5mm input. If I set the mixer’s output to -50 it should output at -30 dBu on the XLR outputs. If I set the GH2 to mic level 1 and give it a 0 dBFs tone i get all eight indicators, and with the -20 dBFs tone I get 4 indicators. So far so good. But when I am recording voices it only goes up to -12 dBFs (on my DAW) and sounds a bit distorted.

My theory is that the input was overloaded, so the AD converter distorted. And after that is was attenuated with 12 dB. The only strange thing is that the 0 dB tone from the 302 did get it to show all eight indicators, I should test the level in my DAW to be sure. Maybe it is the limiter that only opens up when there is a longer full load or something?

So my next test was to put the mixer on -56 and the GH2 to mic level 2. Now the distortion should dissapear as the input is 6 dBu lower while the recording should be +13-6=7 dB louder. Now my -20 dB tone reads as -20 dBFs on my DAW. Again, it gives 4 (and sometimes 5) bars on the camera, which is correct as it’s just around -18 dBFs. The 0 dB tone gives all eight bars, as expected. Recorded sound goes up to -6 dBFs and sounds a lot less distorted. I’m not sure if the distortion has disappeared completely.

I think the +13 is around the native input level, without digitally amplifying or attenuating the signal. I guess I could try to patch it to +7 or something to see what happens, and I might have to attenuate the 302’s output a bit more. It’s not possible from the menu, so i’ll need to use a plug for that. To be continued.

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Posted in: GH2