Getting Decent Audio Out Of The Blackmagic 4K Production Camera

bmpc audio meters

Last week, Blackmagic announced that their v1.9 firmware update for the 4K Production Camera would include audio meters. This was met with great rejoicing by camera purchasers who have been struggling with the amazingly bad audio functionality of this otherwise exemplary device.

Let me preface what follows by mentioning that I have used a lot of cameras and audio equipment over the last 20 years, and the Blackmagic Production Camera is by far the absolute worst. Not only are the onboard preamps noisier than the worst DSLR – meaning that using anything more than 10% gain will result in audio so full of hiss that is almost totally unusable – but the input tolerance seems to have been calibrated for some kind of alien technology. Every type of signal I fed into it was either clipped or inaudible – and often both!

Armed with the new audio meters, I resolved to test the BMPC’s finicky sound circuits more systematically.

After some preliminary testing, I concluded the following:

1) The BMPC seems to apply extremely harsh compression to any input source, such that any signal of desirable volume sounds harshly clipped.

2) The onboard preamps really are useless. You’re far better off amplifying the signal in post-production than in the camera.

3) Even under optimal circumstances, the BMPC audio is far noisier than the files captured by an inexpensive audio recorder.

To illustrate these points, consider the following tests, which were done using the Tascam DR-40 to feed the BMPC.

DR-40 Recorder Tests

Reference files were recorded on the Tascam DR-40, and then everything was normalized to 0db in Premiere Pro in order to determine what a usable final output would sound like.

For the first test, I plugged a shotgun mic into the DR-40, and – as I normally would, when recording audio – adjusted the DR-40’s gain setting so that the audio meters were peaking at about -12db. This was a gain setting of about “30” on the DR-40. I then plugged the “headphone/line” output of the DR-40 into the input of the BMPC. I set the BMPC to “Mic” input, and set the gain to 5% in order to have the meters hitting at about -12db on the camera. As you can hear, the incoming signal was too hot for the camera, and the audio is clipped (although the 4% gain means that there was very little added hiss).

Now, many of you are scoffing at me for setting the BMPC audio input to “Mic” instead of “Line,” when I’m obviously coming out of a jack labeled “Line.” Well, there’s a reason for that, which test #2 will illustrate.

The DR-40 setup for test #2 was the same as in #1, but this time the BMPC was set to “Line.” However, I had to crank the gain up to 100% in order to get a usable level on the camera (around -18db). The hiss, as you can hear, is quite bad. The reason for this is that the BMPC is (seemingly) looking for a +4db line level, rather than the much lower-voltage signal coming from the headphone jack (more about that in a moment).

For the third test, I returned the BMPC input setting to “Mic” at 5%, and turned the gain on the Tascam DR-40 down to “10.” Although the recorded audio level was very low, once the file was normalized, it yielded the cleanest sound.

Here’s the control file: this is what the normalized audio for all three tests looked like, from the files recorded on the DR-40. As you can see, there’s virtually no difference in the waveforms (in fact, you probably can’t tell where each test begin and ends, just by looking at the spectrum view).

bmpc audio test dr40 waveform

Now, here’s what the normalized audio for all three tests looked like, from the files recorded on the BMPC. Here, you can plainly see the clipping in the first test, and all the additional noise (hiss) in the second test.

bmpc audio test waveform

Here’s what it sounded like. You can hear the unacceptable quality of audio from tests #1 and #2.

bmpc audio tests

FMX-42 Mixer Tests

But wait, there’s more!

Since the DR-40 is not the only audio device in town, I pulled out my Azden FMX-42 mixer, and tried plugging it into the BMPC. To make a long story short, the most successful combination of settings was coming out of the 1/8″ -36db jack on the mixer and setting the BMPC to 4%. This seems to be equivalent to the setup for test #3, which tells me that the headphone jack of the DR-40 is probably calibrated to about -35db as well.

Interestingly, taking the +4db line output of the Azden, and feeding it into the BMPC set to “Line” input, still wasn’t great. Since the signal going to the camera was a higher voltage (compared to the -36db “line” from the DR-40), I only had to turn the gain up to about 30% in order to obtain a decent (-18db) signal, so it yielded an okay (although noticeably noisier) result, as you can see and hear in the spectrum view and audio file below.

bmpc azden audio test

bmpc azden audio test

Conclusion

At this point, I would still consider any audio recorded on the BMPC to be a backup for dual-system sound (and/or a sync track). The safest approach seems to be to send a low-volume signal to the camera from the headphone/-36db output of an audio device, and to record on both.

I would be very interested to know if anyone else has gotten better results. If you have, let me know how you did it!

  3 comments for “Getting Decent Audio Out Of The Blackmagic 4K Production Camera

  1. August 14, 2014 at 4:49 am

    Hi Alex!
    Great review! I am doing a Documentary on a Carnival’s Band in Cologne using the BMPC4K and recording audio has been a pain if you want to record directly to the camera. I didnt have time to look in to the audio like you did but I experienced similar problems and I found similar solutions. I used a Zoom H2N as audio device but I didnt plug in any shotgun mic. I thought the zoom was quite helpful because it lets you use its calibration mode (blinking rec button) to let the audio go from microphone to cam. I thought this way I wouldnt have to record to the SD card on the Zoom and synchronize afterwards… First I was shocked by the noise, gain and clipping of the camera! I corrected similar to what you did going really down on the input levels of the camera – I even went down to 1% (which sometimes isnt easy in that touchscreen…). And I played around with the input levels of the Zoom.. but with the different sound levels of the (brass) band when playing or talking to each other it was quite a challenge to find the correct audio setup. In the end I recorded everything quite silently. I could hear what was going on over my headphones pluged into the BMPC, but when I had a quick look on my macbook it was hard to hear anything. I will go into postproduction of the sound today and hope I will manage to turn up the levels like you did. So your review gives me some hope. Anyways – my conclusion is: recording to both and then synchronizing. Blackmagic: please have a look at your audio soon!

    Thanks for the review again Alex. Bookmarked your page! Great work!

    • Alexander
      August 14, 2014 at 5:56 am

      Thanks for the comments! I’m surprised more people aren’t complaining about this. One word of warning: if you record TOO LOW on the Zoom, you’ll have lots of hiss when you boost it in post. It’s a very tricky balancing act, but I am going to err on the side of recording with good levels on the Zoom, and letting the BMPC do the best it can. As long as I can sync the tracks in Pluraleyes, it doesn’t really matter how bad the BMPC audio is … It just makes me nervous not to have a high quality backup track!

  2. DWCoop
    May 14, 2015 at 12:12 am

    this was definitely useful. Even though I found my own solution. I haven’t tried it yet but I’ll let you know how it went the day of the shoot. I have a few laptops and like O.A.I’m going to record my audio through my shotgun Mic but using my pre amp I use to record song vocals. I already started shooting my film called life is lyrics and I’m so mad that this problem haven’t been fixed with some type of update. like what you said I’m sure it’s a hardware issue. Blackmagic hasn’t been focus on the bmcc they already have issues with. Instead they continue to make more camera’s and want more people to buy their products. Personally I love the image quality from this camera. I’ve never been happier with my footage. But I’m am a audio man. And when the audio sounds like shit I feel like shit. Plus I’m a one man band doing the footage and recording audio. It’s a nightmare but somebody gotta do it right? I say you should buy a portal preamp from guitar center that support phantom power cables a little laptop ( netbook or airBook) a professional boom pole , use whatever shotgun microphone you already have and go portable recording studio. Im not going use the inputs on the camera period and use the boxy sounding audio from the cameras internal microphone to referenceing audio when lining it up. Once again. I’ll let you know if it worked for me and will link a video for all the bmpc 4k users That’s looking for a solution. I’m disappointed in black magic for releasing a great camera crappy audio system. Even Canons t3i without a microphone connect to it sounds amazing. Wish they had a cheap 4k camera on the market. global shutter is a power element with this camera. So the bmpc has its perks as well.

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