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BMCC 2.5K with audio inputs used

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Larry Wheeler
BMCC 2.5K with audio inputs used
on May 20, 2013 at 3:51:40 pm

I am a new user to the BMCC. Just got the 2.5K unit in, and started using the TRS audio inputs and ran into a rather odd issue. When I plugged in to the camera with TRS I noticed on the SDI monitor, a constant audio level at about -12 in both channels. With NO audio coming in, as it had no source yet plugged in. This was just the cable!

When I recorded it like that, playback revealed it was recorded that way as well, however, there is no audible sound, and when I look at the waveforms in Audition, there isn't a corresponding visual that shows that constant level. This was true via the Thunderbolt connection to the computer as well. The file recorded to the SSD is the same situation.

All that said, the audio is clean, and true. Whatever is creating this audio level, is not audible, but seems to show up on the level meter LIVE, and played back on the recording. This is not the case with the in camera mic at all, it's normal all the way. No constant level.

The problem I have is that I cannot really set a level with a mic input, as I have to have a signal over -12 to even see it register on the SDI level meter. This is with both channels set ar 57% gain on the BMCC, by the way. Moving the level this way does affect this level, but not that much, unless run at 0%. Even when I switch it to LINE level it does drop out on the meters temporarily, and at same gain, comes back to about -22 level.

Any thoughts would be very much appreciated! I have lots to shoot that involves microphones VERY SOON!


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Peter J. DeCrescenzo
Re: BMCC 2.5K with audio inputs used
on May 20, 2013 at 4:22:25 pm

Hi Larry: I'm not sure what's causing the result you're seeing (I don't have a HD-SDI monitor with audio level display), but if you're running firmware 1.2, I wonder if it could be the DC offset issue?

Firmware 1.2 caused a DC offset audio problem that has been either completely or mostly addressed in the current firmware 1.3, available from the support page on BMD's website:
http://www.blackmagicdesign.com/support/

However, before you install 1.3, note that it introduced an issue of its own: Low frequencies are rolled-off quite a bit with firmware 1.3. However, you can recover these relatively easily in post by boosting the low freqs. So, just an FYI.

There's quite a bit of info about BMCC's audio capabilities in a thread on BMD's own forum (see especially Chris Hocking's most recent, very detailed posts):
http://forum.blackmagicdesign.com/viewtopic.php?f=2&t=7829

Meanwhile, here's an example of my own recording of a Sennheiser ME64 mic via an old SoundDevices MixPre (line level) into a BMCC running firmware 1.2 (see my notes on the Vimeo page for settings details for firmware 1.2; you'll use different settings under 1.3):


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Larry Wheeler
Re: BMCC 2.5K with audio inputs used
on May 20, 2013 at 4:26:02 pm

I assume I am on 1.3 Firmware. Not really clear how to check it. Forgive my ignorance, JUST got this camera, and had studied far more on the video end of it, prior to today. Thank you for your quick response and great insight! Gonna start reading it right now!!!


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Matthew Sonnenfeld
Re: BMCC 2.5K with audio inputs used
on May 22, 2013 at 5:09:33 pm

When did you get your camera? Assuming you are on firmware version 1.3 then you should not have the DC offset issue, but yes you would have the reduced low end which you definitely should be aware of.

This is definitely interesting though. I will have to run a test at home to see if I am getting the same thing. I am running a MixPre-D into my BMCC and I monitor through a Zacuto EVF looping through a HyperDeck Shuttle to get the HDMI. I suppose it's possible that I'm getting the same thing and didn't notice. I'll check this tonight and get back to you.

Is there any difference in where you are hitting levels if you adjust the gain on the camera? Everything is set properly in terms of what should be Mic is Mic and what should be Line is Line? Does it happen regardless if it is Mic or Line level?

In theory the TRS should be giving you the exact same thing as a line level with an XLR. Where else did you see this before as mentioned in your original post?

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Larry Wheeler
Re: BMCC 2.5K with audio inputs used
on May 22, 2013 at 5:21:45 pm

I got the camera two weeks ago, and according to my software, the firmware is up to date. I have to assume it's on 1.3. I have studied the problem a bit more since my first post. It really doesn't harm your audio at all, seemingly. Whatever the frequency of the sound is, it's below 31hz, and can be lessened by EQ. When you adjust gain levels in camera, it does slightly affect the levels, but it won't go away until you go completely zero level. This is ONLY with TRS, and it definitely shows up via Thunderbolt connection, SDI OUT, and on the recordings in ProRes, and RAW. You don't hear it through headphones, and I still don't see it in any waveforms, but it's level shows up, even in audition. I am no audio guy, I can't precisely figure out the frequency of the sound. It looks on a meter, so consistent, like TONE being put in. When you switch to LINE level, it changes the level a few db, but it's still there. I have done this with several cables, a juicedlink riggy assist pre-amp, and plugging directly to the mics themselves, and the same problem occurs. It's biggest problem is that it hides the level of sound as you see it. So proper audio levels on set can't really be accomplished, which is frustrating. I would assume as well, it would mess with level meters on NLE's as well, showing a constant level. Not sure though, I haven't loaded any of the affected footage into an editor. Even when it's opened in QT7, it's showing up.


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Matthew Sonnenfeld
Re: BMCC 2.5K with audio inputs used
on May 23, 2013 at 8:35:51 pm

Does it happen when you just have the cables plugged in? Does there even need to be a mic attached or is it purely a baseline as soon as there is a cable plugged into the jack?

Have you tried with different mics?

Do you have it set to have Channel 2 use Channel 1 audio?

Can you please give me an outline of your general purpose set up? If possible I will recreate at home as best I can.

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Larry Wheeler
Re: BMCC 2.5K with audio inputs used
on May 23, 2013 at 8:53:27 pm

It adds the noise as soon as any cable is plugged in. This is true with no mic hooked up, a shotgun mic, sennheiser wireless receiver, riggy assist pre-amp, or just a cable. The level starts the second a TRS is plugged in.


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Larry Wheeler
Re: BMCC 2.5K with audio inputs used
on May 23, 2013 at 8:58:31 pm

The gains being set to match on 1 & 2 doesn't affect it. If no cable is plugged in to a channel, it won't add the noise. If you make them match levels, both will have the noise. My rig is basically sennheiser wireless lavalier on channel 1 via TRS, and a shotgun mic on TRS 2. Preferably via Riggy Assist Pre-amp to show levels, but can be done directly with either.


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Matthew Sonnenfeld
Re: BMCC 2.5K with audio inputs used
on May 23, 2013 at 9:03:03 pm

Okay, very interesting. I will check at home with mine tonight and let you know what I find.

Blackmagic Cinema Camera, RED Scarlet-X, Panasonic HPX170, Canon 7D
2011 Macbook Pro 17", 2.3 Ghz Quad Core, 16GB RAM
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Matthew Sonnenfeld
Re: BMCC 2.5K with audio inputs used
on May 24, 2013 at 2:49:31 pm

Hi Larry,

I tried with my BMCC on firmware version 1.2. When I plugged in my TRS cables I was also getting noise but on Line level (which is my preference coming from a Sound Devices MixPre-D), I couldn't get the background noise to get above -30db. With no sound coming into the camera, the background noise was a direct function of of the channel gain set in camera, i.e., if I turned the gain down to 0, the noise went away, at 100% it went to -30db, and anywhere in between depending on how I set the sliders. I also did not hear anything in headphones.

It sounds to me like there are definitely gain issues in the camera's preamps that are causing a huge lack of uniformity among the product. Oddly enough, I can't get my levels to 0 ever. Not sure if this is something that anyone else has experienced, but when I sent tone from the MixPre-D at 0db, I can't set the camera to match the level and always have softer camera audio than I am getting in the mixer. So while your levels are too hot, mine aren't hot enough. The background noise if you ask me may just be electronics and power that is sent to the TRS jacks when the camera notices a cable plugged in that is creating a low frequency noise floor. The variation of the level of the noise floor is because of the variation in the sensitivity of the preamps.

Maybe there is a whole other problem to investigate?

Blackmagic Cinema Camera, RED Scarlet-X, Panasonic HPX170, Canon 7D
2011 Macbook Pro 17", 2.3 Ghz Quad Core, 16GB RAM
AJA IoXT
Adobe Production Premium CS6, Avid Symphony 6, Final Cut Pro Studio 3
The College of William and Mary


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Larry Wheeler
Re: BMCC 2.5K with audio inputs used
on May 24, 2013 at 2:56:28 pm

Wow, thank you so much for looking into this like you have! I REALLY appreciate that! I suspect this is a problem just with this camera. Unfortunately, I have to live with it, for now. Taking this one overseas for 13 days, and have no time to sort out this rather odd issue. I am bringing along a separate PIX 240 with XLR in to record audio (and ProRes via SDI) and serve as a redundant recorder, for a super critical shoot in the field. Thankfully, most of our shooting on this trip doesn't require external audio. Once I get back, I will get with BMD for some solution to this odd issue. I really appreciate your looking into this as you have. Thank you!


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Matthew Sonnenfeld
Re: BMCC 2.5K with audio inputs used
on May 24, 2013 at 7:54:54 pm

Just glad to help! I agree with you that this is probably a BMC specific problem. I think the PIX 240 will be a godsend for you as that seems to be the more reliable device. At least you will have the image that you want paired with the sound that you want. I will probably be calling BMD tonight to notify them of the issue and will update you on what I hear back from them. Honestly I'm glad we've investigated it this far because I never would have known about it! Gotta the the COW!

Blackmagic Cinema Camera, RED Scarlet-X, Panasonic HPX170, Canon 7D
2011 Macbook Pro 17", 2.3 Ghz Quad Core, 16GB RAM
AJA IoXT
Adobe Production Premium CS6, Avid Symphony 6, Final Cut Pro Studio 3
The College of William and Mary


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Geoff Addis
Re: BMCC 2.5K with audio inputs used
on May 29, 2013 at 2:52:35 pm

What happens if you short the ring and tip connectors to ground (outer shielding of the lead) ?

What happens if you terminat the mic inputs with 200Ohm resistors?

Have you tried putting a ferrite ring around the mic lead, close to the input jack on the camera?

It could be an RF problem or the pre amp in the camera 'hooting' due to a high impedence input.


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Richard Martz
Re: BMCC 2.5K with audio inputs used
on Nov 27, 2013 at 3:28:25 am

I've been following these audio issues with a keen interest. I'm wondering why Blackmagic would release a camera with all these audio issues. I only began investigating what I should do to solve my own audio problems with the BMCC and was assuming I was doing something wrong. Would anyone like to join in a class action lawsuit? I'm meeting with my attorney tomorrow.

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Anand Vyas
Re: BMCC 2.5K with audio inputs used
on Jan 24, 2014 at 1:42:27 am

Blackmagic Design promised us an image on par with RED Cameras at a fraction of the price. They produced excellent results. You can always use an external recorder and to to be honest using the Riggy Assist I have no trouble using my BMCC with "in camera" sound routed from my Riggy Assist with any good mic. Furthermore the Super 16mm (close to) crop factor makes Focus pulling easier while simultaneously allowing one to use large apertures and still have a nice shallow but controllable depth of field as one as one person trying to use a follow focus is critical. Last words they did not promise the audio would be "perfect" and even if the image wasn't simply incredible, a class action lawsuit is the dumbest thing on the planet. This small company is helping the little guy make GOOD LOOKING FILMS and you want us to help you sue them ? Um, no thanks. Thats the dumbest idea I have ever heard for the most irrational reasons (your inexperience and lack of understanding the camera are the culprit regardless).


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Richard Martz
Re: BMCC 2.5K with audio inputs used
on Jan 24, 2014 at 2:07:14 am

Thanks for the admonition. You are right. Everyone needs grace (unmerited favor). And nothing technical is perfect. So I should learn to temper my expectations. I love the BMCC and the more I use it the more impressed I am with the performance of the camera. I was really just kidding with my comments - although I did actually have lunch with my attorney that day. To forgive is divine. I hope to receive forgiveness from everyone for my coarse comment. Well stated. And noted.

Sincerely,
Richard Martz

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Atlanta, GA

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Richard Martz
Re: BMCC 2.5K with audio inputs used
on Jan 24, 2014 at 2:30:13 am

This sounds pretty stupid but you might want to check to be absolutely sure that your 1/4" TRS inputs are pushed in all the way. When we initially tried this we had the same problem only to discover that we needed to be more agressive about plugging in those cables.

Bot other people have reported the same problem. We only know that the audio is pretty good and we have had no problems getting usable audio. We generally record double system sound as a backup though. Eliminates the nervousness.

Sincerely,
Richard Martz

MagicMartz Media
Atlanta, GA

FCP 7
FCP X
Blackmagic Cinema Camera
ADOBE CREATIVE SUITE CC
Premiere Pro
DaVinci Resolve 9.0
MAC 8 core
After Effects
PhotoShop
Illustrator
Sony HD Cameras
24' Camera Crane with Motorhead
8' jib arm
20K watts of lighting
Multitrack audio
Teleprompters
Grip Truck/trailer
Location video monitoring
Door and hood mounts
Lots of other Fun Stuff!


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