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Old July 9th, 2009, 06:27 PM   #1
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Red audio testing: curious results and a workaround

I've done location audio on a few shoots with the Red One in the past year and have had some puzzling results.

When sending line-level audio to the Red, the Red seems way too sensitive.
I used the same setup I use to record to Panasonic HVX-200s, HPX-170s, HPX-500s, DVX-100s, Sony PD-150s and 170s and JVC HD100s, but when setting up a "normal" gain structure, the Red's recorded audio is clipped.

So, with the gracious assistance of Sunshine Whitton, owner of AbsoluteTechnology, and the use of his camera for an hour, I tried to find out what was going on and develop a workaround.

First off, we tested on a Red One with Build 20 software, an updated audio board and the newer XLR-to-mini-XLR cables that he got with the audio board upgrade.

For the testing, we only used audio channels 1 and 2.
Each channel was set to line level input and the input level sub-selection was set to 0 db.

I used my Sound Devices 442 mixer with a Sennheiser MKH-416 on channel 1 and a Sennheiser G2 wireless mic on channel 2.
Channel 1 was panned full left and channel 2 was panned full right.
The connection to the Red from the 442 was a Remote Audio breakaway cable with headphone return.

The SD 442's output limiter was set to kick in at +17 db on the meter, 3 db below the factory default of +20 db.

The 442's master output level pot was set to unity gain ( at the detent ).

The SD 442's output level on the 'A' output bus was confirmed to be line level.

Again, this is no different than my usual setup.

Sending tone to the Red from the 442 resulted in green bars on the audio metering display that stopped at the first vertical white line ( reading from left to right ).

This, I've read, should nominally be -20db on the Red.

I also recorded to my Edirol R4-Pro hard disk recorder via the SD 442's direct outputs. Once again, tone from the SD 442 was set to the -20b line on the recorder's LCD meters.

I then had Sunshine do some normal-level talking and some shouting.

Even normal conversation was clipped on the Red, while the Edirol handled it perfectly. Shouting resulted in the Red clipping badly and the Edirol still not clipping.
As Ty Ford would say: "It had hair all over it..."


First Workaround
-----------------

I had two Shure 15/20/30 db switchable in-line attenuators.
I set them at 15 db and put them between the output of the snake and the Red's mini-XLR adapter cables.

We recorded a second time with normal conversation and with shouting.

This time, the Red didn't clip.
It looked like levels were a bit lower than I would have liked to see, but at least the audio was preserved.
Just guessing here, but I bet a 10 db attenuator would have been perfect.

When I pulled the Red clips into Vegas 9, it seemed like the shouted passages were peaking around -7.8 to -9 when the 15 db attenuators were in use.


Second Workaround
-------------------

We pulled the attenuators out of the signal path and I tried turning down the master output level on the SD 442.
This could be made to work.
When I set it to about 9 o'clock, the Red levels seemed to work out ok.

The problem with this approach is that it's not really a calibrated, repeatable mechanism.
I tend not to like "set it about there and try it again" stuff.
It might work in a pinch.

It seems like it messed up my gain structure and I wouldn't feel comfortable doing that.

Conclusion:
-----------

The Red One's audio input isn't like the other cameras that are in common use.
1 khz tone may line up ok, but normal line-level audio is too "hot" for the Red's input section.

A good way to settle things down may just be to use 10 db in-line attenuators.

Perhaps the Red folks will add a line-level pot or something, someday.

Cheers,

Stephen H

Last edited by Stephen Hall; July 9th, 2009 at 06:28 PM. Reason: grammar
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Old July 9th, 2009, 07:33 PM   #2
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Maybe the Red one's line level inputs are Consumer line level -10. Or they have a similar problem to what Sony had with Betacam decks ipnuts way back when and Shure had to change the way their line outputs worked to work well with them. Changing the output impedance was one solution but the real explanation was much more complicated. Do all mixers have the problem or are some different and why?
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Old July 9th, 2009, 09:08 PM   #3
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Well that's funny. I was at the Trew Audio workflow seminar last month here in Toronto, and we had a guy from Production Services tell us that we wouldn't need the -10db pads on the new build and audio board. It was also stated on RAMPS that we don't need the -10db pads a few days ago.

RED cam still stinks for audio. Sooner or later they'll get it right.. hopefully.
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Old July 10th, 2009, 05:58 AM   #4
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Sound Devices' site has a technical report article on their testing of the Red ... Audio Performance of the Red Camera (Red One)|Sound Notes|Sound Devices, LLC and it verifies that the native input level without the special attenuating cables is about -10dB @ 600 ohm impedance. They also recommend making up pads that place 1 kilohm resistors in the signal hot and cold lines (XLR pins 2 and 3) as a better option than the RED supplied cables.
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Old July 10th, 2009, 10:44 AM   #5
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That article is excellent, but the testing was performed over a year ago and it's likely that the camera they used probably had the original audio board. It would be interesting to know what current hardware and builds require.
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Old July 11th, 2009, 09:41 PM   #6
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I've had two experiences with the RED, ranging from frustrating to disastrous. It's hard to believe that one company could screw up in so many different ways with that camera.
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Old July 13th, 2009, 11:52 AM   #7
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screw up and still be the darling of the video crowd.

Regards,

Ty Ford
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Old July 13th, 2009, 02:03 PM   #8
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I've used the newest build and never could get useable audio from it. There was always a little distortion on peaks, even though the levels looked fine. It's especially frustrating because there is no control over the gain on the line inputs.
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Old July 13th, 2009, 02:13 PM   #9
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I don't think many people care all that much about getting usable audio from the RED. It seems to be stepping in as a replacement for small film cameras. And in that regard, the workflow is already based around running dual system.

Heck, my camera (and audio recorder) don't even lock, and I still shoot dual system. I use wild sound from the on-camera mic just to help with sync later, but I wouldn't use in-camera audio unless it was a dire scenario.
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Old July 13th, 2009, 06:56 PM   #10
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Quote:
Originally Posted by Perrone Ford View Post
I don't think many people care all that much about getting usable audio from the RED.
Yes, but this excuse is getting pretty old and tired. It is not even a matter of cost saving in many cases (changing the value of a couple resistors would fix the level problem, no impact upon cost).

This is about video designers being so cavalier and uncaring about audio design that they are unwilling to even look at practices that have been standard in audio design for decades, most of which have little or no impact upon cost.

Tell me, how would you feel about buying a new car (even a low cost one) that used the same ignition system as a Model T? That is about how long most of this has been standardized in audio.

-Mike
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Old July 13th, 2009, 07:25 PM   #11
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Quote:
Originally Posted by Mike Demmers View Post
Yes, but this excuse is getting pretty old and tired. It is not even a matter of cost saving in many cases (changing the value of a couple resistors would fix the level problem, no impact upon cost).

This is about video designers being so cavalier and uncaring about audio design that they are unwilling to even look at practices that have been standard in audio design for decades, most of which have little or no impact upon cost.

Tell me, how would you feel about buying a new car (even a low cost one) that used the same ignition system as a Model T? That is about how long most of this has been standardized in audio.

-Mike
Dude, if you feel strongly about it, don't support them. Easily solved. I just don't hear anyone complaining about ARRI and their audio. And how long have THEY been around?

Frankly I think RED should have left Audio off the camera. If you're going to put it on the camera, it should work at least as well as the handycams.
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Old July 13th, 2009, 07:54 PM   #12
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Despite the audio snags, I'm a huge fan of the Red One. The images are incredible and it's given indie filmmakers a shot at quality that most could only dream about.

If the camera audio section is less-than-stellar, I can live with it -- I just want to find a workable solution. I think using 10 db inline pads are going to make the audio problems recede into the background.

I look at it like a Panaflex using mag-stripe film stock or something. The picture's the thing.

Cheers,

Stephen H
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Old July 13th, 2009, 07:57 PM   #13
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Now if indies only cared as much about content.....


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Old July 13th, 2009, 08:41 PM   #14
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Originally Posted by Perrone Ford View Post
Dude, if you feel strongly about it, don't support them. Easily solved. I just don't hear anyone complaining about ARRI and their audio. And how long have THEY been around?

Frankly I think RED should have left Audio off the camera. If you're going to put it on the camera, it should work at least as well as the handycams.
I think ARRi is a slightly different market.

Part of the problem is that these are complaints of audio people. But these are not the people who buy and spec these cameras. Until the people that do spec them - the video people - complain loudly about these problems, the manufacturers have no particular reason to listen.

Yes, they would have been better off to just leave it off rather than do it wrong.

This is like havng an auxilliary jack on your camera which is a BNC marked 'video out' which you have never had a need to use. But one day you need it for an extra feed the director requested. No problem, just send that to any standard video monitor, right? You do so, but the video is competely blown out and rolling. None of the adjustments on the high quality, professional monitor seem to have enough range to fix this problem. Finally, in desperation, with expensive people standing around, you call the manufacturer and find out that either a special cable which you do not have is needed, or one has to be made up, because, despite the fact that NTSC outs on all other cameras are 1V P-P, this one is 2V P-P.

That is the sort of situation this stuff places audio people in.

I say these things in a video forum on the bare hope that some maufacturers might see the problem and fix it. Or that some of the image oriented people might know that this can cause them production problems too, and maybe it would be a good idea to start letting the manufacturers know that they consider audio important.

The Red is used in professional situations, and in rental situations, where unexpected incompatibilities can cause people a lot of grief.

-MD
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Old July 13th, 2009, 09:05 PM   #15
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Mike, it's not like I don't get what you're saying. I came from an audio and still camera background to video. I owned a posting studio so I hear ya. But seriously, who rents a $50k package and records sound to camera? Not "just because", but as a matter of workflow. I don't do that with my $7500 camera. And honestly, I don't feel the RED is a different market than the ARRI 435/235. I think that's exactly the market.

But I think the RED gets a pass because it produces gorgeous images. In years of reading, I have never once heard anyone mention the sound on a Viper, SI2K, Genesis, Dalsa, or any similar cam. Do those cameras even have audio hookups?

I can imagine a production where someone rents a RED unseen and untested and doesn't know about the audio issues, but honestly, at this level, you ought to spend at LEAST a day or two pre-shoot to work out any kinks. If the DP/Operator don't do camera tests before a production, there is no one to blame but themselves. I thought it was a matter of course to do camera, lighting, and audio tests with stand ins for at least one scene to make sure everything was solid before production started. I surely wouldn't show up on film day one with a full crew and actors not having checked my gear.
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