Hi Everyone,

I am trying to work out the optimal setup for connecting our Sound Devices 302 Mixer to our Blackmagic Cinema Camera.

For those of you that haven't worked with this camera before, let's just say the audio side of it is "interesting" (i.e. DC offsets, inconsistent levels between two channels, no real control of settings, etc.).

My instinct tells me that I should just be sending line level out of the mixer, and set the camera to line level as well. However, when I do this - even with the camera's levels set to 100%, the signal is still too soft. I assume this has to do with Sound Devices and BMD deciding on different definitions of "line level" (i.e. +6 dBu vs +4 dBu vs -10dBV).

Currently the best configuration I can get working nicely is the following:

BMC
Microphone Input: 0
Ch 1 and Ch 2 Input Levels: Mic
Ch 1 Input: 28%
Ch 2 Input: 28%
Headphone Level: 90%

302
XLR Atten. Level: -40dB
Everything else is factory default.

By keeping the input level down on the BMC - it also seems to keep the DC offset to a minimum.

This seems to work fine, and records decent levels - but I'd still love to try and get a line level signal working.

I know you have lots of attenuation control on the 302, which is great for padding down a mic-level output - however is there any option to INCREASE the gain of the line level output (i.e. +4dB)? I've looked through the manual a number of times now, and I can't see any way of doing this - so I'm guessing you simply can't, which makes me think I think to come up with another solution.

Looking at the forums - it seems like there are plenty of other people who are successfully sending line level signals out of their 744Ts, etc. to the camera without any issues - so maybe I'm missing something really obvious.

Here's some other interesting things I've discovered, that may be of some help to others:

- It seems the DC Offset really messes with UltraScope (which is the only way to actually get a audio meter on the camera). For example, if you're not sending ANY audio to the camera, the meters will still read -25dB in UltraScope. However if you capture this audio, and then remove the DC offset - you'll see it's actually at infinity. Given this - UltraScope isn't really helpful at all for lining up reference tone or monitoring.

- MediaExpress also seems to have a mind of it's own. Some times the meters seem to be acting correct - other times, they're way off.

- The headphone jack on the camera is useless. When you compare what's being recorded to what's being monitored via the headphones - you can notice such a big difference. You loose a lot of the lower-end when using the headphone jack.

- The camera is incredibly temperamental and easily confused. If something SHOULD be working, but it doesn't seem to be - chances are you're not going crazy. A simple re-boot will fix most issues it seems. In fact, with the current firmware, I would go as far as to say each time you change the audio settings, you should exit the MENU then restart the camera to make sure they have actually been activated.

I have some screenshots on the Blackmagic Forums (http://forum.blackmagicdesign.com/viewtopic.php?f=2&t=7124) if that's of any help.

Any comments, or suggestions would be hugely appreciated.

Thanks in advance!

Best Regards, Chris!

What kind of jacks are you using?

Somewhere deep in my memory there is a comment from an audio guy I saw somewhere, that they need to be stereo jacks and soldiered in a certain way, or you get a week signal.

I first used mono jacks and get less than stellar results from my Wendt mixer at line level.
Than I got the Juicedlink Riggi and it works fine for me with the supplied cable at mic level (besides the DC offset) and never tried the Wendt since than.

But maybe you want look into those jacks again and make sure they are stereo and proper cabled for a balanced connection.

Frank

Thanks for your reply Frank - greatly appreciated! I think you might be exactly right...

We're using a custom-built multi-core cable (2 x XLR + Headphone on 302 end, to 5-pin XLR).

However... as a temporary solution, we were originally using a Sound Devices XL-10 break-out adapter (5-pin XLR to 2 x XML & 1 x Headphone), and 2 x XLR to Jack cables as adapters. I have no idea how the XLR to Jack cables were wired - so maybe that was the issue?

We're now using a custom-built 5-pin XLR to 2 x Jack & Headphone - so it should all be perfectly wired (the guy who made it up for us is a audio cable genius).

So if there was originally an audio cable issue - hopefully that's now resolved (unfortunately I don't have the old cables with me to test).

After playing around with the new cables though, I'm still not ENTIRELY happy.

Based on the tests I've done this morning, this is what I've found to be the "optimum" settings:

BMC
Microphone Input: 0
Ch 1 and Ch 2 Input Levels: Line
Ch 1 Input: 76%
Ch 2 Input: 76%
Headphone Level: 100%

302
XLR Atten. Level: 0dB
Everything else is factory default.

...however, although this setting seems to ensure that nothing will clip on the camera - the noise floor is very high.

When I was using Mic Level - it seems the camera worked best when you had the levels on the camera around the 25-30% range (this also helped keep the DC offset to a minimum).

I would love to keep the levels at around 25-30% on the camera - but there's simply not enough gain coming out of the 302 on line level.

I'll keep playing... but if anyone has any ideas, let me know!

Best Regards, Chris!

Are you sure, those jacks are STEREO jacks?

The need to be 3 tiped - ie TWO black rings.

http://images.beglec.cdn1.be/product/1301/800/1.jpg

And they need to be wired like this: http://www.mediacollege.com/audio/connection/xlr-jack-stereo.html

IMO, the only digital 'cinema camera' that will record 'usable' audio is the Arri Alexa. (of coarse.. "usable" is subjective)
I frequently send audio (scratch/sync track) to REDs. The Epic and Scarlett have bizarre audio inputs as well. I'll take a look at the BMC manual when I get chance and state my findings.

PS- How are the cooling fans in the BMC?

Way quieter than anything Red.

Frank - I'll triple check tomorrow, but yes, as far as I know our new breakout cable is wired as you described. Have you tried running Line Level into the camera at all?

Rick - Although I agree that using an external recorder (i.e. 744T, etc.) will maintain the best quality, and should be the preferred workflow whenever possible - there are times when recording straight to the camera makes the most sense.

In terms of fan noise, the Blackmagic Camera is actually pretty quiet, all things considered. I haven't done any proper tests, but at a guess, I'd say it's probably even quieter than an Alexa.

Thanks for all your help!

Check out Robert Rozacks analysis at his juiced link blog.

http://www.dvinfo.net/forum/blackmagic-cinema-camera/515081-sound-black-magic-cinema-camera.html

I have good sound using mics into juiced link and out from juiced link at mic level. BMCC also set at mic level set at about 30%. then adjust preamp level monitoing for distortion out of camera phone jacks.. Remember also that BMCC does not have power for mic and you must have power provided by your preamp or mixer if your mic does not have power.

Thanks for your reply Chris. Yes, I have watched that video - and it is very helpful.

However, my concern with using Mic Level is that the BMC "freaks out" if you send it a signal that's too hot, and then automatically switches to Line Level and you can't switch back until you restart the camera (or even worse... actually shuts down the audio completely if you leave the hot signal going for too long - requiring a camera restart to get audio back).

This shouldn't really be a problem, if you have an external mixer and set up your gain structure and limiters properly - however, we've noticed that simply disconnecting and reconnecting our break-out cable causes the camera to think the signal is too hot, and automatically switches from Mic to Line without any user interaction (requiring a restart). This is just plain annoying.

Keeping everything at line level in theory will be the best option for quality and to avoid the firmware limitations. In practise however... maybe not?

I guess I just need to do some more tests, and see if Mic Level actually achieves better results.

As far as I can tell, the juicedLink tests on the video were all doing using Mic Level settings on the camera - so it would be really interesting to see if they get similar results with a Line Level setting. Given all the strangeness with DC Offsets depending on the level controls - I wouldn't be surprised if the camera acted completely differently in Line Level than it does for Mic Level.

Having said all this... I have been able to get decent recordings using both Mic and Line Level. But, what I'm trying to do is find the BEST solution where the maximum quality is kept.

As far as I can see, the juicedLink low-noise preamplifier's only output Mic Level - so this explains why the video and their blog posts only talk about the Mic Level performance.

Please correct me if I've said anything that's incorrect!

I found the simple tests I have done with that set up pretty clean.

Then there is this thread over at the Black Magic Forum:

Blackmagic Forum • View topic - Firmware 1.3 better audio performance (http://forum.blackmagicdesign.com/viewtopic.php?f=2&t=7498)

The original poster there is saying that firmware upgrade 1.3 actually corrected some of the issues with audio, and that the percentage scales recommended by Robert Rozack and others must be adjusted.

If true, the weird thing is that Black Magic did not announce that change.

I'll do some more tests later today with the updated firmware and see what I can find! Exciting!

The original poster there is saying that firmware upgrade 1.3 actually corrected some of the issues with audio, and that the percentage scales recommended by Robert Rozack and others must be adjusted.

If true, the weird thing is that Black Magic did not announce that change.

I just did some tests - and I can happily confirm that the firmware update DOES in fact fix some of the audio bugs!

I have documented all of my tests over on the forum post you linked to if you want to check them out.

I agree - it's incredibly strange that BMD made these changes, but didn't actually tell anyone! I have no idea why.

Sound Devices 302 has long had this issue of the line output of 0DBu being low on some cameras which are expecting usual Line level of +4DBu as level. This was true of Canon XLH1 as well as others. Often input adjustments on the camera would take care of this but some cameras would be noisier than others when set so high. I thought they had a way of getting to +4DBu output on the Sound Devices in Menu but maybe not. Of course you could try letting the tone be set lower on the camera meter and then run the levels on the mixer a little hotter when recording and see if that gives you the results you want. One of the problems of standards not really being followed by the manufacturers.

Thanks Daniel. Good suggestions!

The BMC 1.3 Firmware update has fixed most of my concerns I think.

100% Line Level on the camera seems to be 0dB Gain/Attenuation, so when you set the 302 to 0dB, everything lines up perfectly.

The recordings on the camera are still fairly noisy - but I think this is due to the camera's circuitry not the 302.

I normally calibrate the levels using "full tone", to ensure that I'm capturing as much as possible.