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http://www.dvxuser.com/V6/showthread.php?325824-Panasonic-discovered-a-fix-for-the-audio-buzz!

I analyzed the GH4 audio buzz issue yesterday. While I couldn't find any issue with the internal mics, the external circuit is picking up camera electronics, primarily the electronic shutter (buzz varies predominantly with shutter speed). I tried a few mics with TS, TRS, and TRRS plugs. The problem is not with the plug itself- the buzz is the same with them all. If the Panasonic DMW-MS2 with TRRS plug really works without the buzz, then there's something going on with resistance and/or capacitance/grounding (or more). Reviews of the DMW-MS2 appear to show that the mic is both noisy and not very directional. It's a mid-side mic however decoding is only available on the mic (and controlled with camera settings). I use an Audio Technica BP4029 stereo shotgun on the FS700 (mid-side) and it's great being able to control the stereo field in post varying from pure directional shotgun (mono) to a wide stereo sound stage, and everything in between. The stereo is so good that listening with headphones on you'll turn around sometimes thinking the sound is live- it can be that 3D (similar to binaural). The current workaround is going back to the standard DSLR method: setting in-camera gain to the lowest and using a preamp. For the GH4 that means setting mic gain to -12dB. At -12dB, the buzz is still present, however when testing with a Sennheiser G3 wireless system starting at -30dB receiver output and going up from there, the buzz seems to take a sharp reduction at around around -18 to -12dB G3 receiver output. Perhaps the GH4 has some form of AGC going on? In any case, at around -12dB (or higher) G3 receiver output, the SNR is high enough that examining the waveform in post shows the buzz is inaudible and audio is then usable. When testing with a Rode NTG-2 on battery with a TRS connector, the noise floor (white noise) isn't that bad on the GH4 (compared to the 5D3 for example). However the motor-boat buzz renders the audio unusable. The buzz is a triangle wave, about 2x the amplitude of the noise floor. More info and waveforms + spectral plots here: http://www.dvxuser.com/V6/showthread.php?324401-External-Microphone-Solutions-for-the-GH4-(avoiding-the-buzz) A low-cost, reasonably small and lightweight solution is an iRig Pre, for about $33. Along with a splitter cable (or with the soldering mod) it is small enough to attach to the back of a shotgun mic with Velcro or a rubber band. With a 9v battery, it supplies phantom power and sufficient gain for clean, high-quality audio.