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Old August 31st, 2007, 04:36 AM   #1
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Hiss, Pop, Bang on XL1

Hi,

I've recently been trying to record a short commercial using my Canon XL1s. The company I worked for suggested hiring some equipment to get a better finished product so we hired, a Vinten Pro5 (lovely), some Arri Redheads (also lovely) and a boom with Sennheiser shotgun mic (can't remember the exact model). As this was my first effort I was unaware that most shotguns require phantom power and would not be directly compatibly with the Canon. So on the first day of the shoot we had to find some kind of Phantom Powering pre-amp. For this we used my Allen & Heath GS1 recording desk. This is where my problems began.

Basically I now had four volume controls to play with. In order from the camera:
1. Canon XL1 recording volume input.
2. Master output from the mixing desk.
3. Volume fader on channel 1 of the mixing desk.
4. Gain control on channel 1 of the mixing desk.

I had real trouble keeping the amount of hiss and noise down on the recording. It seemed turning the XL1 recording volume up past 10% created huge amounts of hiss and hum and obviously keeping that down and turning the gain up on the desk introduced a lot of clipping.

Basically what I'm asking is which volume control should I be using to increase and decrease audio level without introducing unwanted noise? As a general rule when I use the mixing desk for close mic-ing, I set both faders (channel and master) to 0-unity gain and then use the gain control on the channel until I get a nice hot signal. I'm also curious as to how sensitive shotgun mics are, do they require much gain? Also why did the XL1 volume control cause such major noise problems?

Thanks in advance

Dave
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Old August 31st, 2007, 05:34 AM   #2
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Sounds like you were sending the hot line level outputs from your desk to low level line or mic level inputs on the camera and overloading them.

I assume you connected the desk's output to the camera RCA audio inputs. Your desk can be set to send either +4dBu pro line level or -10dBv consumer line level outputs. The camera's RCA input are rated for the various menu options to either -11dBv (LINE), -35dBv (MIC ATT), or -55dBv (MIC). Obviously the combination that best matches is to set the desk to send a -10dBv output to the camera's RCA inputs set to LINE. The next step needs some source of tone to align everything - an inexpensive "tone-plug" on one of the desk's mic inputs would work well. Set the desk's master output fader to the unity gain mark and it would normally just sit there from this point on. Set the input channel fader to unity and turn on the tone plug. Adjust that input channel's gain (trim) control until the output reads 0VU on the desk's meters. In the camera make sure it's on manual level and adjust the recording level controls so it reads -18dBFS (EBU standards) on the camera meters. You might want to tape off the level controls so they can't accidently be moved. Connect your mics to their channels, set the faders to unity, and adjust the mic gain controls one at a time until they're bouncing around 0VU on the meters during dialog rehearsal. Use the channel strip faders to ride gain during the shot so dialog hovers around the 0VU mark and your signal to the camera and its own level controls should be like Goldilocks' favourite porridge - just right <grin>. The camera op should see voice peaks bouncing up around the -12 red dot mark on the camera meter or a tad higher. Final tuning of the levels should be done in post.
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Old August 31st, 2007, 06:09 AM   #3
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Spanktastic!

Thanks, that's what I needed.

That is exactly what was happening, just checked the menu setting, it was set to Mic, so to use my mixer I have set it to Line.

Dave
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Old August 31st, 2007, 07:30 AM   #4
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Don't forget to also make sure you're using a -10dBv output from the mixer as well so "line" = "line" and don't neglect to align things as I suggested. Just setting the mixer to a "hot" output level is inviting problems as the digital levels in the camera are very unforgiving of overs.
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