Audio Level Padding to Prevent Distortion

Recently, I shot a live performance and, afterwards when reviewing the footage, I found that I had audio overload problems. I had used my Lumix GH4 with the Panasonic DMW-MS2 microphone and this simple setup just wasn’t equal to the task. The problem was the great dynamic range of the show which included actors and a singer. It was a small venue and when the singer was up close during a crescendo the recorded signal was very loud and badly distorted. Conversely, during quiet moments when the performers were at the other end of the stage or facing the opposite direction the level was too low.

You can clearly see where the waveform has clipped (the current time indicator is right in the middle of a clipped section).

You can clearly see where the waveform has clipped (the current time indicator is right in the middle of a clipped section).
Of course, one thing that would help in a situation like this would be to mike all the performers and set appropriate levels. In this case, that just wasn’t an option. And, it still might not have solved the dynamic range problem completely.

Two-Level Audio Recording

Red arrow shows the switch that turns on/off the juicedLink preamp’s -16db padding feature

I’ve since figured out a pretty good solution for this kind of scenario and it doesn’t involve miking each performer. My solution was to buy a juicedLink Riggy-Micro preamp and use its second channel -16 db pad feature. When recording in mono on the left channel you can set the right channel to output the same signal but at a level 16 db lower. This way you have two levels to choose from in post. As long as the left channel doesn’t overload you can use it. But, if it does, you can fall back on the right channel and then adjust the gain in post to an appropriate level. It’s like exposure bracketing for audio.

Left channel on top, right channel below was recorded automatically at -16db

This shows what the waveform looks like when capturing a mono signal at the two gain levels.

I’ve tried this a couple of times and it’s worked out well so far. I just choose whichever channel is better, copy it, and paste it into the other channel. It does create more work in post but everything is a compromise, right?

Problems with the Panasonic DMW-MS2 microphone

In my particular case my solution presented another problem beyond the increased workflow complexity. What I didn’t realize when I ordered the preamp is that my Panasonic mike won’t work with it (or any other analog preamp). The DMW-MS2 is designed to be plugged directly into the camera. When connected directly to the camera it offers some nice features like software selectable response patterns (shotgun, super shotgun, stereo, or lens angle tracking). But, as far as I can tell, the microphone only works when plugged directly into a compatible Panasonic camera like the GH4.

For me, this means I have to use my backup microphone, a lower quality off-brand unit, when I want to use the juicedLink preamp for audio bracketing. So, there’s a word to the wise if you’re considering the Panasonic mike. If you’re sure you’ll never need to use it with an external preamp or audio recorder it will probably work just fine for you. Otherwise, you might be better off with another microphone.

Comments 4

Larry Cunningham

June 30, 2015 at 8:41 am

Hey David,
Glad you found a solution for the over modulated audio. That is pretty slick. But what I wanted to ask you is about the Lumix GH4. I ordered it from B&H and tested it out in daylight shots with low ISO and slow shutter speeds, but when I looked at the images at 100% I was blown away with the excessive grain. Have you had any issues like that? No matter what ISO I use there was excessive grain. Any thoughts?

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David Salahi
June 30, 2015 at 9:07 am

Hi Larry,
I guess it depends on what you mean by “excessive.” I haven’t been shooting stills very much lately. l’ve been shooting mostly video and I do see some noise and sometimes it’s very noticeable at the high ISOs (up to 3200) I’m often forced to use. But, in general, when shooting video at low ISOs I’ve been pretty happy. I took a still shot out in my garden just now to have a close look at the noise. This was handheld at ISO 400. f6.3, 1/100. It’s a small crop from the overall Raw image, saved with PNG-24 so no loss in the compression. Straight out of camera, no adjustment at all. I can see some noise, particularly in the darker areas, but I don’t think I’d call it excessive. How does this compare with your experience?

Dave

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David Salahi
July 1, 2015 at 8:19 am

Larry,
As a point of comparison, here’s another shot of my Alpinia which is very similar to the previous shot from my GH4. This one is from my Nikon D7000 and was taken last year; ISO 320, f5.0, 1/250. Again, this is a crop of an unprocessed image, saved in PNG24. This one looks, to me, slightly less noisy than the shot from my GH4. And the Nikon shot is at a slightly lower ISO. As another point of reference, the D7000’s APS-C sensor is larger than the GH4’s Micro 4/3. I have heard others complain about the GH4’s noise but mostly in the context of video and it’s harder to pin down in a video than in a still. I’m still curious to know what results you’re getting.
Regards,
Dave

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