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Old December 21st, 2009, 11:44 AM   #1
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5D2 (dSLR), Line Level to Mic Level?

Hi all,
I am about to get a padded cable made to take a Sound Devices Mixpre's XLR's line level to the 5D's mic level, but don't know how much padding would be needed. Some say -40db, some say -50...
Does anyone know what the sweet spot is for the cam? As I think the mixer is +4db out(?), I should be able to make some simple math and come up with the right padding... Mind you, this is not from Mixpre's 1/8 TRS Tape Out, but from XLRs which are supposed to be hotter and also of course sturdier - hence the choice of going with them over 1/8 Tape Out.

All best,
David
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Old December 21st, 2009, 05:47 PM   #2
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How big would such an XLR cable/adapter wind up being? Trew Audio has the Shure inline attenuator Shure A15LA Line Adapter - Problem Solvers - Mic Accessories - Trew Audio then you still need a cable. Seems kind of bulky compared to the -25dB Pinknoise or -50dB DVcreators line to mic 1/8" cable.
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Old December 22nd, 2009, 08:26 PM   #3
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It wouldn't be that big. One (not me) can fit in the resistors and what else is needed inside the XLRs, so would look like the one in the bottom of this link:
Remote Audio: DV Cam Cables

But I still need to know how much padding would be needed... So pls, anyone out that who knows?

Happy Holidays or whatever you are up these days,
D.
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Old December 22nd, 2009, 09:35 PM   #4
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Typically you want to attenuate the line level by 40db.

You can buy and adjustable attenuator like this:

Hosa ATT448 Input Attenuator, XLR Male - XLR Female, 3-way Switchable | Full Compass
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Old December 23rd, 2009, 01:03 AM   #5
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We had to do that trick David is talking about when the On Cam mic was switched with a battery powered mic, that obviously had a lot more level then the mic that came on the camera.
At first i thought it was the Mic itself crasy $600 thing that didnt sound much better than the cheaper ones we were using. i though the mic itself was breaking up from to much sound (rock n' roll at parties), the on cam mic never had that problem.

Just like your saying we just dropped some resistance in, i actually thought it was quite rude, you know something some audio guy would say i had broken the 33rd commandment over :-)

Because it was a problem ONLY with very high sound output things, and I did not want to reduce the sensitivity and volume for other things, AND because i was totally guessing then testing what REALITy would hit me with at the job, i put a Micro 2 Way center off toggle switch to have different settings, Right into the Rubber Strain relief on the XLR connector itself.

We just shoved the mic up right next to the speakers of my stereo, cranked up the stereo and tested resistances, We might have used a POT to test the resistance, then measure the pot to see what we came up with.

I got 2 Values for resistance that i thought would work, and it has been there ever since, music gets to loud, i just switch it to middle, music gets louder i switch it down, when i dont want the trim on, the switch in the up position would make a direct connect.

3 Poles on the switch, one the resister is active when the switch is in the center off position. One side its just a resister to get to the pole, and the last pole is direct connect. You probably wouldnt want direct ever.
Soldered everything good, tested at all levels of sounds, did a hard pull test to make sure the solder held, and finished by shrinking the heat shrink wrap around it. The toggle sticks out of the top of the rubber releif thing it doesnt change the size, and it is barely visable. because it is in a Pocket on that camera it doesnt get Accidentally hit and changed.

I was thinking about using a trimmer pot or a 10 turn pot which would fit in the same situation, but pots can get worse over time and crakle a bit, so i picked solid.
with this i had High, Med, and low and i can switch it quick without even taking my eye off the viewfinder. An adapter thing in that situaion would have been completly kludge in the way, and not an optionat all, compared to my Kludge :-)

DB ?? who cares, if i had used math and set some specific known by math and science values i would still have to test test test, so i didnt use that kind of thinking. If i had chose some single "perfect" setting it would not have worked in every situation.

I assume that is what your trying to do?
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Last edited by Marty Welk; December 23rd, 2009 at 01:43 AM.
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Old December 23rd, 2009, 03:57 AM   #6
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Thanks for the elaborate post.
But is this what I want to do?
Hmmm, not really. Well both yes and no. Thing is I will have a proper preamp/mixer in between the mic(s) and 5D2. So, idea is to turn off cam gain completely and then my mics wont be near hot enough. But the nice Sounddeviced preamp/mixer will bring them up to level.
I am thinking since I will go via mixer/preamp, that I can keep a "constant" nice level to feed into cam, but preamp as it is is too hot at +4db(I have heard) and then some people say consumer mic in is -40 db, so pay should be 40-45db - does that ring a bell to anyone here? I am not an audio tech, just a stills photographer wanting to add some nice vid to a long term project, I am working on.

Best,
D.
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Old December 23rd, 2009, 04:33 AM   #7
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You have XLR input mics into the mixer , not adapted 1/8" mics right?
so the mixer itself is now working competly as it would, with the meter representing the level of the mics as they are properly adjusted. everything is as it should be there?

Then there are 2 styles of output out of the mixer, the Balanced XLR outputs (now preamped) and the Tape out 1/8" unbalanced 1V P-P line level?

THe Mixer is capable of Gaining the sound some 56dB , but you still really want the meters to read correct on the mixer right?

The camera item has in it a 1/8" unbalanced input that can be switched between Mic and a Line level 1V P-P signal right?

then you want to feed the XLR balanced output into a 1/8" unbalanced input?



Side notes: (dont bother reading this)
dB as used frequently by audio electronics, and in digital programs, is not sound pressure anymore :-) and in digital it is really rediculous to see that term still being used to Backwards our thinking.
It is like using the Term ISO in a CMOS camera that has no film, so all the dinasours can find the watering hole.

of course all that being subjective, the point being is your really working with differences in Miliwatts and Voltages and all, not sound pressures. which can also be represented in dBm dBv but it wont help to do that.
Decibel - Wikipedia, the free encyclopedia
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Last edited by Marty Welk; December 23rd, 2009 at 05:17 AM.
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Old December 23rd, 2009, 06:42 AM   #8
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Hi Marty,
yes to everything. And I am sure you are right about the db not making sense in digital age as well - I dunno much about audio, except I want a proper hot signal to go from mixer to 5D, so that 5D doesn't have to preamp anything.
But yes to "metered" preamped XLRs going into mic level of cam through a 1/8 TRS. I will use Magic Lantern to turn off any cam gain.
Do you think it is just the 40db padding...?
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Old December 23rd, 2009, 07:24 AM   #9
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Alas, you may just have to try it.

I've always been under the impression that a line --> mic pad should be 50db or even 60. But it could be, under your specific conditions (5D2), that 40 is correct. Sorry, dunno.

Maybe ask Sound Devices?
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Old December 23rd, 2009, 07:32 AM   #10
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i still dont have the lingo down here .
padding in english means to add something :-) although that can also mean to add in insulation.
when your saying padding here, you mean attenuating? to reduce,.lessen, to make smaller?
more weird techno terms that get passed around and mean new things.
would we not be professional to say Lower, cut , trim, or limit :-)

and if your going to "pad" by attenuation wouldnt you be padding by Minus some ammount of "dB" things

also doesnt the mixer itself have Level adjustments for the line out?
If the mixer is within 10Feet or so of the camera, there is no reason i can think of to use the XLR outs and try and adapt even if you still have to attenuate. Which looks like it can be done appropriatly by the mixer itself.
your actually adding in more things that can go wrong, with adaptions. and even though XLR is "professional" its design was for the purpose of going LONG distances, and surviving. and to screw us all into paying 5 times as much :-)

more that i dont understand, especially when we have some stuff here that has never seen an XLR and can make better sound :-) just not with very long wires to it.
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Old December 23rd, 2009, 07:43 AM   #11
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Yes, I mean to attennuate. When correctly metered, the preamp will send a signal that is way too hot for the 5D to handle. 5D has mic level in, Preamp/mixer has line level. So, I need to pad that level down to mic level, but just trying to figure out the best value.
I was hoping someone had run a Sound Devices or another line level device to the 5D and could tell me, how they'd done it.

Come to think about it, I will try to move this post or repost inside the proper 5D section, I just realized now, that there was such a thing...
Thanks for all the answers though.

Cheers,
D.
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Old December 23rd, 2009, 07:53 AM   #12
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I would just test for myself, by running mics and different levels of music crammed in them.
WHY?
Because i would want the lowest signal to noise ratio, which means i want a good signal.
because different things are calibrated different.
because what works for one person might only be working, and they might not have noticed weird stuff going on like limiters, AVCs, distortion. and they might not have provided range into the red which it might end up getting everyonce in a while.

if you going to limit the input , really you should trim it with Adjustable resitance, and then test the heck out of it with some FULL range of music, not some 1Htz tone or some useless test item. when you find the sweet spot, you take it just a tiny bit down from there.
then
you will not only have the fullest range, a safe range for all circumstances, a calibration for your actual instruments , but you also will have full assurances and no surprises when some sound or voice or different circumstances ruin your sound.


that is what i am trying to say.
and it is a 2 wire connection (for each stereo side) to set up the adjustment, which doesnt qualify as being any more technical, than conneting up the things your already connecting.
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Old December 23rd, 2009, 08:58 AM   #13
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David,

Yah know, I was kinda re-thinking your strategy--even with this, is the cam going to give you decent quality? I know the reason that most people do dual system with DSLRs is to avoid the AVC that you will be disabling but, I'm thinking the analog portions of the cam might not be that great.

Marty,

A mic attenuator has been called a pad since forever. Yes, technically, you should specify it with a negative sign, but that is pretty much assumed.
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Old December 23rd, 2009, 09:53 PM   #14
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Yes an attenuator is called a pad and yes the negative is assumed, or it wouldn't be attenuation and there is no one fixed value.

You find most hard wired pads are -40db, but for a correct match it depends more on the impedance difference between what the line output is looking for and the load presented to the mic input.

Here's a great resource if you want to get it right.

Uneeda Audio - Build your own attenuator pads
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Old December 23rd, 2009, 10:03 PM   #15
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Maybe I should mention that I started in pro audio 30 years ago. The first pro video camera I used was to SONY tethered to a 1/2" tape deck with 8.25" reels. So the info I'm offering is based on a lifetime of experience.

When shooting with a DSLR I typically run a Sound Devices 302 into a Marantz PDM661. I take the unbalanced line out, attenuate it and feed the 5DII or 7D mic input. I replace the track in FCP with the 661 recording.
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