BMCC audio - thoughts on affordable and reasonable solutions

I wanted to find out whether in camera audio is an option with the BMCC at all and what efforts make sense. So I did some tests on my own. Over the last month I just experimented with some stuff I had and used my ears (and some meters). I don’t claim this to be scientific or comprehensive but it might help others to find their own solution.

In case you need a comprehensive overview concerning the audio issues and possible solutions you might want to refer to this well written thread by Chris which was my starting point.


1) Testing with my studio gear. Where are the limits?

I connected my TC Studio Konnekt 48 and my Mackie Mixer to the BMCC. Both deliver balanced studio levels at +4dB and have plenty of gain. The result: You can get good audio recoding in the BMCC – if your signal is predictable and does not exceed a certain dynamic range.

The signal to noise ratio of the BMCC is about -60 dB (same as most external recorders in the affordable price range). While that is quite enough for processed soundtracks and many recording situations it defeats the headroom advantage of 24 bit recording. No way to work with a decent headroom if the noise is lingering at -60 dB. To put this in relation: my interface and Mixer have an SNR of about -90dB. But there is a price to it: to provide a good low noise audio path you need power and decent hardware. There is a reason why Mackie does not rely on cheep wall mount supplies, why Sound Devices Mixers are that expensive and (I guess) why JuicedLink delivers »only« Mic Level.

Bottom line: The BMCC provides audio recording on par with other affordable devices (with limited dynamic range). If you need studio quality recording, you need something else (in the range way above the affordable handheld recorders).

But what about the frequency response?
[solved in Firmware 1.8!]
While the frequency response of the BMCC is ridiculous and should have been fixed long time ago, in practice I honestly don’t care. Bass control is part of any audio workflow. It’s the same effort to cut bass (like I do with all other recordings) or boost it for the BMCC (as documented by others: the bass is attenuated in the digital domain and therefor easy to recover).


2) What is reasonable?

As the dynamic range of the BMCC’s audio is limited, it makes no sense to me to invest 500$ or even more for a preamp. Boosting your signal out of the noise floor is a nice concept until you hit the end of the dynamic range. I’d rather save for a Sound Devices 552 or something like that and look for an affordable interim solution.


3) Trying my Zoom H2n

I made me a custom cable and plugged the device into the BMCC. It works, but only on a low level. The H2n (as most devices of its class) outputs consumer level (-10 dB), the BMCC expects studio level (+4 dB). You'll get a signal that is in real world usage (leaving some headroom on the Zoom) about 20 dB below what you want. It sounds better than the build in mic and is usable for syncing or some ambient sounds (think airport . But it introduces too much noise if pushed up in post to dialog level.

I also tried to set the BMCC to Mic instead of line and to about 40%. It’s possible to get something usable out of this setup, but I would not trust it. SNR is okay, but sending a line signal to a mic input is neither technical ideal (impedance miss-match) nor will it prevent clipping at lower levels. According to my testing the attenuation of the BMCC is at least partly in the digital domain. I got some clipping even if the signal was way below 0 dB.


4) The bulky solution: my good old Mackie

If portability is not important and I have a power socket close by, I simply take my Mackie mixer with me (a fifteen years old 1202-VLZ pro). It gives me enough gain to amplify even old ribbon mics to studio level, decent knobs, flexibility and big bright LED meters. According to my tests aiming for +7 dB (the last green LED) for peak gives a nice level on the BMCC. You can get those mixers used for under 200$ and the little brother comes new in that range (stay away from cheaper clones).


5) The portable solution: Art usb dual pre

This unit is a »mixed bag«, but with some fiddling it fills my needs for a very decent price (below 100$).

The good things:
obviously the price, it has XLR and TSR inputs, analog potentiometers, phantom power and is designed to output balanced studio level via TRS (exactly what the BMCC asks for). It can be powered by 12V (like the BMCC), by usb and by 9V battery. In my tests I got about 2 hours from a 9 V LiMH battery with phantom power on. A feature that is not documented but handy: if battery is low, both channel’s green LED are dimly lit.

The problematic issues:

• Metering only provides two LEDs and the green one is set a little bit too high (-10dB). The red one is supposed to be 0 dB with 6 dB headroom before clipping the analog stage. Together that gives you 16dB visuals before clipping. That means: when you »see« that you’ve got something coming in, it’s almost time to reduce the gain. Not ideal but better than no meters (I’m looking at you, BMCC).
• While it claims to have 48dB gain, only about 30dB are usable without introducing noise. That is more than enough to boost my Zoom H2n, but it is not sufficient to bring an average small condenser mic (like the KM 184 or an Octava MK 012) up to studio level. But as the Art is a dual channel pre-amp you can use both channels in a row: just plug the output of channel one to the input of channel two and add some more gain. Works like a charm with no added noise.
• No rigging option. I drilled some holes into the case and screwed it onto a quick release plate.

6) On camera recording

While not ideal, in some situation it is the only possibility or at least handy to mount your mic on the BMCC.

I sometimes simply mount my H2n on the BMCC as replacement for the horrible built in Mic when I only need sync sound (just using the Zoom as Mic). I also use it sometimes for ambient sound (recording in Mid-Side mode to be flexible in post) in addition to a boom mic. In this case I send the mid signal of the Zoom to one channel of the BMCC and the boom mic to the other and record into the zoom as well. If I don’t need atmo I stick to the internal sound, if I need more, I sync the files from the Zoom.

I also used my Octava MK 012 mounted on the BMCC in some situations.


The key to on camera sound is to know its limitation and to have a decent shock mount. I found the Rycote shock mount (in my case the invision INV-7-HG-MARK III) does a good job reducing handling and fan noise from the BMCC. It takes my H2n or any of my mics.


7) One risk remains: loosing connection

With all the above I have flexible, affordable solutions to get decent in camera audio in most situations. The only thing that remains: Without any indication of incoming audio and an almost unusable headphone out on the BMCC you might notice that broken cable or a not properly inserted TSR-plug when it is too late.
I really am looking forward to the announced update with audio metering.

Johannes

Awesome read. Thanks for sharing Johannes!

Great post, I have the art dual pre and know exactly what u mean about it adding noise past 30db gain. That's a brilliant idea to use both preamps. I'll give it a try (although I just bought a dr-40 last week which has been great so far.)

Thanks for that bit of info Johannes. It's great to see so many folks sharing this sort of info with the masses.

I am very new to this Blackmagic Cinema 2.5 Camera and to film-making frankly. But here we are with this camera and my head is spinning reading this thread.

In laymen's terms, what is the most basic way to upgrade the audio for someone who, believe it or not, just wants to use this camera to learn the process and do some basic short films? We need something fairly user friendly.

I am looking on Amazon for external mikes and there are several for the "pocket" version, but nothing for the Blackmagic Cinema 2.5 Camera.

Thanks in advance for your indulgence.

Matt, I missed your post until now. Have you found some answers? Otherwise I''ll try to give some later.

Johannes

I did some quick re-testing with 1.8.

1) The frequency response is much better now. There is still a bass rolloff, but now it is where it makes sense (and where every audio engineer would put it in 99% of all real world recordings): approximately 80 Hz. So very usable now in that aspect.

2) The dynamic range seems unchanged, so signal to noise ration is still at -60dB (like in any other budged recorder). So usable but not in the professional class - but that class stuff would neither fit into the body nor the price range of the bmcc.

(I have not checked the internal mic (you would'n check image quality without a lens, would you?)

Bottom line: good progress where possible, no wonders otherwise.

Now we only need audio meters (or at least some indication that audio is coming in at healthy levels) and we can move on.

I am very new to this Blackmagic Cinema 2.5 Camera and to film-making frankly. But here we are with this camera and my head is spinning reading this thread.

In laymen's terms, what is the most basic way to upgrade the audio for someone who, believe it or not, just wants to use this camera to learn the process and do some basic short films? We need something fairly user friendly.

I am looking on Amazon for external mikes and there are several for the "pocket" version, but nothing for the Blackmagic Cinema 2.5 Camera.

Thanks in advance for your indulgence.

Matt,

for general purpose atmosphere audio I'm using the Rode Stereo Video Mic Pro
(http://www.amazon.com/Rode-Stereo-Video ... eo+Mic+Pro) and after first short tests I'm getting really good results with firmware 1.8.

But of course this won't be sufficient for indoors in a quiet environment (as the BMC is quite loud and even with a shotgun mic mounted on the camera I got its fan-noise recorded in a quiet environment) but you could always just connect a mic with a longer cable to the BMC and place the mic near the source of sound.

It depends on what you're after and which levels of quality you expect.

You might want to look at the Sony PCM-M10 Linear PCM Recorder. The SN is 87dB or above (1kHz IHP-A). At Amazon it is $250 with a 32GB SD card.

My wife uses it for recording her singing so it is easy to use and has a lot of features.

Steven, do you use your wife's voice on your videos? Any samples? I'm thinking of using vocals by one of my daughter's that I'd previously recorded.


Sent from my iPad using Tapatalk

Hi

I was just given the same pre-amp that was used in your set up. I was wondering if you can show more pictures or tell me how you hooked it up. I'm sure it's pretty simple but I work best with visuals and instructions. When I figure stuff out on my own i usually screw it up