Topic: Help me mod a MixPre?

[NonFiction]

Okay, I'll betray my ignorance on this stuff, but here's the setup:

I want to use a SD MixPre with a Canon Xh-A1 camera. The Canon is a bit weird in its audio section, in that it wants a +10dB line in signal. I sent a query to Sound Devices that went like this:

<<You inquired:
++++++++++++++++++++++++++++++++++++++++++++++++
I'm hoping you have a good solution to the problem of connecting the Line level outs from the MixPre into the Canon XH-A1, which if I understand correctly, wants a +10dB line in signal, whereas the MixPre puts out a +4dB line level. Ideally I would like to avoid using the camera's so-so mic preamps to get the best sound possible into the camera. Do you guys have an easy solution for this? I don't have the MixPre yet, but will buy if I can be assured of a good solution. I plan to mount the mixer more or less full-time to the cam. Thank you for your help!

SD Answers...
++++++++++++++++++++++++++++++++++++++++++++++++
The MixPre is a Mic level In, Line Level Out device. There really is not any way to boost or attenuate the outputs. Our slightly larger mixers have the capability, but not the MixPre. Is there any way to attenuate the input of your camera without switching to Mic? +10 seems like a very hot level to default to.
Reply.
>>

So, Looking around the video sites, I see some people using the combo with usable results. But not a lot.

I'm inclined to leave well enough alone. Well, actually I'm not. Not after seeing/hearing some of the results you guys are getting by hot rodding your kit.

So I'm wondering is there something obvious I could/should do to calibrate the MixPre to my camera? Furthermore, if such a solution exists, would it be possible to make it switchable/undoable so I can readily use it with other recorders?

I'm a bit awestruck by the level of the conversation around here. Any advice on this will be appreciated.

[stirinthesauce]

+10db is scorchin hot.  If I had to take a guess, I'm betting the +10db signal is the max that the canon cam can take.  I would venture to say you would have no issues taking a signal of less than +10db.

Just a not so educated guess, as I have no cam experience, just pro audio experience, and a hack at that 

[DSatz]

Are you using the mini-jack input or the XLRs?

The brochure on Canon USA's Web site says about the stereo mini input:
A/V1: ø 3.5mm mini-jack (audio and video), -10 dBV/47 kohms

For the XLR inputs it says:
ATT: 20dB, -59.5 dBV (Auto mode)/10 kohms
(LINE/MIC switch set to LINE), Max 1: -71.5 dBV
(Auto mode, XLR GAIN UP at 12 dB), Max 2: -71.5 dBV
(manual mode, max. volume), Max 3: -83.5 dBV
(manual mode, max. volume, XLR GAIN UP at 12 dB)

... which is harder to interpret, but I don't see anything about +10 anywhere, which would be completely unheard of (and a horrible design choice) as a nominal signal level.

--best regards

[NonFiction]

Thanks for the replies. Sounds like I might be getting somewhere. 

The goal is to run the signal from the MixPre via XLR into the camera's Line In, to circumvent crummy onboard preamps.

I'm new enough to sound that talking about +10 vs +4dB is mostly untrodden ground for me, so forgive me if I'm parsing others' info badly. I'll copy in a couple links to online discussions by folks trying to use this combination (with some success evidently):

http://www.dvxuser.com/V6/archive/index.php/t-96563.html

I've had an email conversation with the OP on this one, who's basically confirmed what he said in the last post--he just runs the line-in with the pots cranked all the way up on the camera and gets acceptable sound. I'm content to give that a try, but wanted to find out if there's maybe not a better way.

http://dvinfo.net/conf/printthread.php?t=91427&pp=40

This second thread seems to be a more thorough discussion. My main goal in this thing is to get the signal up generally, with a good limiter inline for occasional peaks. I shoot documentary and interviews, and some music. If I have a pre with a good, unobtrusive limiter, I feel like I could run a good beefy signal and rarely hit the limiter (but it's there when I need it). Maybe I'm barking up the wrong tree with the MixPre anyhow? Or does it seem like a good solution.

Thanks for the brainpower...

[esteyes]

i am wondering if there is some confusion over the 10 db number being tossed around... perhaps nonfiction got mislead by someone/thing and really means to be saying -10db which would seem to correspond to what the specs are for the camera as well as the common consumer/prosumer level for audio vs the +4db level for pro audio

Consumer audio equipment line levels are rated in dBV, and the most commonly used nominal level for such equipment is −10.00 dBV, which corresponds to a sine wave of about 0.3162 root mean square volts (VRMS). The absolute reference voltage is 1.000 VRMS.[1] This reference voltage represents 1.000 milliwatt (mW) at 1.000 kilohm (kΩ).

Professional audio equipment line levels are rated in dBu, and the most commonly used nominal level for such equipment is +4.000 dBu, which corresponds to a sine wave of about 1.228 VRMS. The absolute reference voltage is 0.7746 VRMS. This reference voltage corresponds to 1.000 mW of power at 600 Ω.

it just seems so coincidental...

as far as testing, he could feed a tone (maybe an mp3 downloaded from somewhere) at 1K Hz and at -10dbv into the camera and see that the levels are at 0db. or where ever they end up and decide from there whether he needs to bump the input signal...

i know nonfiction plans to use the XLR outs of the mixpre, but i thought i would mention the following:
one thing i have seen as i do feed a camera very often is that the camera levels are low when the camera is fed a consumer (unbalanced -10db) signal into the balanced xlr inputs. this is normal because you are only feeding the summing amp in the camera pre with 1/2 of the signal it is expecting to see. unbalanced to balanced cables have only pin2 hot on the XLR, pin1 & 3 are tied to ground (well sometimes pin3 is blank). things return to normal when i return to either XLR>XLR or go MINI>MINI

neil

[DSatz]

Non, without an actual camera here to test, unfortunately I can't figure out which of the various people in those discussion threads are giving accurate information. The people who are doubting what the other people are saying have very logical-sounding reasons for their doubts.

But let's not kill the messengers--sometimes in the real world a product is designed in an obtuse, seemingly almost insane way. This is particularly true when a product straddles the line between the consumer and professional categories and while I hate to make generalizations like this, it seems to happen far more often with Japanese-designed products than with European- or American-designed ones. I've just seen it too many times by now--ask me some time about my almost-$3000 Sony TCD-D10 Pro DAT recorder, which I certainly wish I'd never bought. On paper it's a fine recorder. In reality, its analog audio electronics are utterly useless.

So I don't want to assume--possibly at substantial expense to you--that this camera's audio line inputs are arranged in any kind of rational way from a professional user's perspective. Maybe they really aren't.

This is the type of situation in which a good relationship with a knowledgeable professional dealer would be worth a lot, no?

--best regards

[NonFiction]

Esteyes and Dsatz, thank you. You're talking sense. Not having the mixer in front of me, I'm naturally at a loss to figure out whether the reported problem is indeed a problem.

Anybody out there in Seattle, would care to have an in-person conversation with me and help figure some of this stuff out? I'll buy the coffee/beer?

Thank you all again.

Scott (NonFiction)

[George2]

I have used the SDMixPre and SD302 going into the Canon A1. With the MixPre I used 40dB attenuators on the output of the Mixpre. On the SD302 I set the output for 50dB attenuation. Both times running in mic level into the A1 and set tone to -20 on camera. The gain pots on the input of the cam were about 12 o'clock, or in the middle, if you can call it the middle of the range... the pots actually turn counter clockwise to increase gain... stupids...... anyway... I listened to the final edit and the sound was fine. There was someone on those forums that actually tested the line in on A1 with SD mixer and camera pots turned wide open... said it sounded good.. about 90dB dynamic ranges.....But I have a thing about cranking pots wide open to get the correct level.....

[NonFiction]

BRH... thank you. So, you're putting the mixer signal into the Camera thru Mic in, so it's getting preamped twice, innit? Obviously the quality of the final sound will determine its usability, and it might well be fine, but this is kind of what I'm trying to avoid.

Yeah, those pots on the camera turning the wrong way really are screwy (they're meant, I think, to be viewed from the back, where up=up and down=down. But that's just not how most people think).

But looking at BRH's signal path, isn't that sound getting jacked around an awful lot, going into a preamp to get it nice and high, out through an attenuator, and in through another (reportedely kind of lesser quality) onboard preamp? I mean, I'm not crazy about running the pots all the way open either. Or is that just how it goes when you put parts together--you do what's needed to get them to play nice?

[George2]

I don't know if the line input on the A1 is going through the mic preamp ..... with a line level pad.... no way to know. Is that switch on the side of the cam switching in a pad and you still go through the preamp??? who knows?
I wasn't worried about any added noise..... I'm mostly worried about "Usable Audio"