BMC & Sound Devices 302

This information might be helpful for anyone trying to get a BMC to play nicely with a Sound Devices 302.

After a lot of experimentation, testing and camera resets, this is the combination we found to work best:

BMC
Microphone Input: 0
Ch 1 and Ch 2 Input Levels: Mic
Ch 1 Input: 25%
Ch 2 Input: 25%
Headphone Level: 100%

302
XLR Atten. Level: 40dB

When outputting 1kHz tone at 0dBu from the 302 to the BMC, it should read -12dB on UltraScopes.

No matter how hard we push the 302, it doesn't seem to switch the BMC back to Line Level, which is great - as I was a little worried each time something accidentally peaked, the camera would either reset to Line Level, or just shut down the audio completely requiring a camera reset.

We've also found that the "Repair DC Offset" function in Adobe Audition CS6 fixes the offset in one click, which is handy.

In terms of audio quality - although definitely not as nice as something like a 744T - it's completely useable.

Now we just all need to beg BMC to PLEASE, PLEASE, PLEASE fix up the audio features in a future firmware release!

Did you test the line input vs the mic input from the 302...

I was going to test the 522 tonight. My first thought was using line level for better S/N.

Has anyone other than the "riggy" designer done any additional tests?

Thanks!

Did you test the line input vs the mic input from the 302 ... I was going to test the 522 tonight. My first thought was using line level for better S/N. ...

My BMCC line level audio test with the SD MixPre (original model, not the "D") which doesn't have mic level out is here:


In addition to JuiceLink's tests, I believe others have also gotten somewhat better results with the BMCC set to mic level rather than line level. However, for my purposes, the results I got were good enough for most productions I work on. And using line level avoids the BMCC auto-switch-to-line-level, um, "feature".

And yes, I agree: I hope BMD improves how audio is handled in their camera(s).

Yes, Line Level would make sense - however I just couldn't get it to work.

If I set the camera to line level, and output a line level signal from the 302, then I need to set the levels on the BMC to 100%, and even then I'm nowhere near on the UltraScopes to a useable level.

The camera basically needs to be set somewhere between 20-30% regardless of Mic vs Line to defeat some of the internal processing and to get a good SNR, but when set to Line, no matter what I tried, I couldn't get a usable signal from the 302 - even if I send a Mic level feed that's highly attenuated.

That said, I will try again and see after shooting today.

Also, if you have a 522 - I'd just send the BMC a guide track for syncing purposes but ACTUALLY use the recordings from the 522. Obviously the 522 will have MUCH better audio.

If you have a timecode generator I'd also suggest sending the timecode to both the 522 and Ch 2 of the BMC to make life easier. Plural Eyes/FCPX is great. Timecode is better.

... If I set the camera to line level, and output a line level signal from the 302, then I need to set the levels on the BMC to 100%, and even then I'm nowhere near on the UltraScopes to a useable level. ...

As noted in the details on the Vimeo page at the link in my previous post, setting the BMCC line level input setting to ~85%, with a line-level signal test tone out of my SD MixPre, resulted in -18db sound level in FCP7. (I don't use UltraScope.)

I think the resulting sound quality I recorded is quite good. Of course, it's not quite as good as what BMD's specs for the BMCC imply, nor as good as what a pro external audio recorder is capable of, but IMHO my BMCC recordings are very useable. YMMV. Cheers.

Interesting! So you were just sending Line Level out of the MixPre with no attenuation, etc?

I'll definitely have to do some more tests later today and see if I can get a nice signal using Line Level.

I wonder which "line" level they are using? -10 db consumer or +4 db professional or +6db professional
http://en.wikipedia.org/wiki/Line_level

I didn't get a chance today to test, finishing a B4 to EF adapter from spare parts to test if I want a "real" one.

I'm interested in having some golden settings for multiple workflows.

The two workflows I'm most interested in getting "good" settings for are:
Dual sound with 522 and BMCC fed external time code.
Boom / Lav fed to BMCC (no TC)

I'm guessing I'll start testing with 25% line setting in BMCC then feed tone at every output level from the 522 to see what's what...

I'll post my results.

I wonder which "line" level they are using? -10 db consumer or +4 db professional or +6db professional ...

Here are the specs for the older-model MixPre I use (now discontinued; not the newer "MixPre-D" model):
http://www.sounddevices.com/products/mixpre/

... finishing a B4 to EF adapter from spare parts to test if I want a "real" one. ...

O.T.: Cool! Let me know how that goes! Cheers!

You've probably seen this:
http://gearjones.com/2011/09/15/abel-ci ... ur-thirds/

B4 lenses can be adapted to work with the BMPCC's 16mm sensor, or (with a doubler) the BMCC's larger sensor, but can't cover the BMPC-4K's S35 sensor.

OK, now back to audio ...
-

If I set the camera to line level, and output a line level signal from the 302, then I need to set the levels on the BMC to 100%, and even then I'm nowhere near on the UltraScopes to a useable level.

Very strange.
I get strong signals from mixpre-d to BMC, go down to 50% in BMC to keep DC offset small,
and the overall sound is very good.

Wow, the audio side of this camera is "interesting"

The line out of my 522 into the BMCC at 50% gives different line levels on CH1 & 2.

There's a 3db difference between channels and the DC offset is also different...
http://www.eyelinemedia.com/audiotest1.jpg

Hmmm...
EDIT_
I just looked at the manual of my 522... the default line out is -30 DB when VU is at zero.

The 25% setting looks correct in sound forge (but with a level difference between channels)
http://www.eyelinemedia.com/522Line_BMCC25_line.jpg

The limiter is set to 20 and I'm guessing I won't get any distortion even just under limit on the 522.

I'll do some program material tests next

The audio I got from the 522 into the BMCC at 25 line sounds fine... after I:

DC offset each channel individually
Normalized to match volume

Then a little Izotope for vanity.

http://www.eyelinemedia.com/program25Ed.mp3

Yup, I should stick to editing, VO is not my gig.


Tram TR50 -> Lectro UM400a -> UCR411a -> Sound Devices 522 (line) -> BMCC line 25%
Wav file opened directly in Sound Forge

The audio I got from the 522 into the BMCC at 25 sounds fine

Is that at Line Level or Mic Level on the BMC?

25% line on BMCC, sorry about being vague. I edited orig post

Great, thanks!

Obviously I need to go back and do some more testing and see if I can get a decent line level signal into the camera!

We noticed the same thing as David - it seems the higher you set the level on the camera, the more difference there is between the the left channel and the right channel - even if you're literally just unplugging the one cable and switching ports. We have also noticed that the level settings have a direct relationship to the DC offset. There's some strange processing going on internally. But once you find the "sweet spot" it works as it should.

We also noticed a couple of times today, when the audio just randomly turned off for no apparent reason. I THINK it's because we were unplugging and re-plugging the breakout cable to the camera occasionally - and I think the "noise" from this disconnect/reconnection is loud enough for the camera to "panic" and just shut down the whole audio system. Restarting the camera is the only fix. So you need to be REALLY careful if you're recording SOLEY to the camera - and keep an very careful ear on the return line. Unfortunately though, the headphone feed on the camera is pretty horrible (very noisy) - so you don't really want to be monitoring the return all the time, as it's not really an accurate representation of what's being recorded.

We'll try do some more detailed tests tomorrow and see what we come up with. If I get time, I might also try hook it up to a 702T, 744T, 552 and 664 to compare results.

I didn't compare the 522 internal recording to the BMCC because I didn't want to know... But I'll end up biting the bullet and witnessing the horror.

I can guarantee I have clients that won't pay for "higher quality" sound and the additional post costs to sync dual sound. Even if I did an A/B between devices they wouldn't care.

But on the bright side, they're going to love the picture and "who cares" about audio anyway.
(The last statement was a joke, I've been a recordist, mixing engineer and musician for 20+ years)

... But on the bright side, they're going to love the picture and "who cares" about audio anyway. ...

As Monty Python says, "Cruel, but fair."



-

I have finally had a chance to do some quick tests...

I have a Sound Devices 302 connected to the BMC (latest firmware) via 2 x XLR to 1/4" Jack cables.

I am sending out "factory default" tone (1kHz tone at 0dBu) from the 302.

Here are my results:

---

TEST ONE

BMC
Microphone Input: 0
Ch 1 and Ch 2 Input Levels: Line
Ch 1 Input: 25%
Ch 2 Input: 25%
Headphone Level: 100%

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

UltraScope

Test One

test1.png (608.56 KiB) Viewed 13727 times

Audition

Test One - Audition

test1_audition.png (175.73 KiB) Viewed 13727 times

If I try and switch the camera from Line to Mic - it simply won't switch, as the signal coming out of the 302 is too hot (instantly triggering the overload protection).

TEST TWO

BMC
Microphone Input: 0
Ch 1 and Ch 2 Input Levels: Mic
Ch 1 Input: 25%
Ch 2 Input: 25%
Headphone Level: 100%

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

UltraScope

Test Two

test2.png (607.48 KiB) Viewed 13727 times

Audition

Test Two - Audition

test2_audition.png (177.8 KiB) Viewed 13727 times

After a lot of messing around, and trying all different kinds of combinations of settings, for whatever reason, this seems to be the best option (at least for me):

---

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.

---

When sending out "factory default" tone (1kHz tone at 0dBu) from the 302 I get the following...

This is what the signal looks like in UltraScope:

UltraScope

ultrascopes.png (588.22 KiB) Viewed 14921 times

This is what the signal looks like in MediaExpress:

MediaExpress

mediaexpress.png (742.06 KiB) Viewed 14921 times

This is what the signal looks like in Audition AFTER applying the "Repair DC Offset" favourite:

Audition

audition.png (178.52 KiB) Viewed 14921 times

---

Here's some interesting things I've discovered:

- It seems the DC Offset really messes with UltraScope. 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.

- Maybe I'm doing something really stupid - but no matter what I try with the 302, I still can't get a decent LINE LEVEL feed into the camera. It's simply not loud enough.

I really hope BMD is listening, and has a firmware update that fixes all these audio issues soon!

In the meantime however... the above configuration seems to be working, and it actually sound pretty good.

When I get some spare time, I'm going to compare the actual recording quality between a 744T and the camera, and see what the difference really is. But for now... ignorance is bliss.

I've just done another test - this time sending Full Scale Tone (where "full scale" is the same as "clipping level") from the 302 to the Camera.

---

BMC
Microphone Input: 0
Ch 1 and Ch 2 Input Levels: Line
Ch 1 Input: 100%
Ch 2 Input: 100%
Headphone Level: 90%

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

UltraScope

UltraScope

Ultrascope.png (609.61 KiB) Viewed 14914 times

MediaExpress

MediaExpress

MediaExpress.png (633.28 KiB) Viewed 14914 times

Audition

Audition

Audition.png (183.56 KiB) Viewed 14914 times

Good news! The latest firmware release seems to fix these issues.

See: viewtopic.php?f=2&t=7539