Blackmagic Cinema Camera Audio Quality: Using External Preamps to Get Better Sound
The folks at juicedLink have already presented us with strong evidence that using the company's Riggy Micro/Assist low-noise pre-amplifier configuration with DSLR shooting has major advantages. First and foremost, it greatly improves the noise-floor performance of on-board recorded audio, even matching high-end dual-system recorders in its signal to noise ratio -- additionally, though, using any good preamp avoids the mobility and convenience you lose with having to use a separate recorder, plus the need to sync in post. Now, juicedLink's Robert Rozak performs another exhaustive test, this time to illustrate the benefits of using the Riggy Micro/Assist setup with Blackmagic's Cinema Camera -- plus major audio issues that must be addressed with that camera system. Check out the video below to see the results.
The video is about 20 minutes long, but I think important to watch for a better understanding of the considerations that BMCC users or on-board audio shooters in general will have to make in the field:
One has to give serious credit to Mr. Rozak and juicedLink here -- they're clearly trying to illustrate the genuine benefits of using preamps to shoot on-board audio at better-than-acceptable quality levels here, all the while explaining important considerations in the audio world, and not just trying to push their products on us. Not to mention the fact that here they're using the results to highlight legitimate concerns with the way the BMCC handles audio recording, and even reaching out to Blackmagic to address them. I for one have great respect for the level playing field they've established to balance the test results, and I think the outcomes here are pretty difficult to argue with.
As far as performance goes, it's once again indisputably clear that, if you have to or want to shoot single-system on-board, a preamp is really the way to go. Now, I'd venture to guess pretty much any dedicated and mountable preamp will give you better results than going straight from the mic into the camera, but obviously juicedLink wants you to hear the advantages of choosing their system over other competitors' similar offerings. What's interesting is that the BMCC design team seems to have kept audio in mind during development -- listen to the non-preamped recording with the BMCC, and you hear how much better its performance is than that of a DSLR. In fact, I'd go as far as saying that non-preamped audio with the BMCC is still actually better even than the DSLR audio recorded using the Riggy Micro/Assist in juicedlink's last shootout.
Where the Cinema Camera falls short in the audio realm is very important to note, however. The most major concern is its audio system's DC offset -- this is a malady pretty easily correctable in post (not that you should have to correct for this at all, under anywhere-near-ideal conditions), but the concern is mainly that it may cause you to mis-calculate your peak levels in a way. Basically, after correcting for the DC offset, you may find that your audio wasn't actually as loud as it was reading -- this is well demonstrated in the video. Additionally, the BMCC uses digital gain and attenuation to manipulate your levels. Robert explains that digital gain increases noise at unacceptable proportions, while digital attenuation decreases headroom, which hurts your signal-to-noise ratio by bringing your levels closer to the noise floor.
Because of these considerations, juicedLink contends that audio bracketing -- the company's innovative use of the same input signal across two separately-dialed channels (one about 16dB lower than the other) which allows you a bit of a safety net if you clip in your primary channel -- is not truly possible with the BMCC. For one thing, juicedLink feels this to be a more adaptable safety measure than something like a limiter, which may have to be calibrated for each camera situation. For another, they claim their 'properly implemented' analog circuitry is far better suited to this practice, and given analog's tendency to bend before breaking, this seems an entirely plausible assertion to me.
Beyond all this, Robert has asked Blackmagic to look at fixing a few issues in firmware updates down the line, including the DC offset. They're also asking for toggle-ready audio metering akin to what Magic Lantern brings to many DSLRs, the removal of an automatic feature which switches the audio from mic to line level when mic level channels clip, and some more intuitive gain/attenuation controls. There's a lot more to find out (and just as importantly, to hear, too) in the video, so I'll leave the rest of the information for Robert to explain.
Were you guys surprised by the BMCC audio recording performance versus that of the DSLRs we're used to? What about the BMCC's shortcomings, particularly its DC offset? Is the investment in a preamp adequately justified to you for on-board audio recording?