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Canon XL1S / XL1 Watchdog
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Old July 11th, 2003, 10:15 PM   #1
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Odd Audio Buzz: Looking for answers/solutions

I just finished a shoot with three XL1Ss. The DP had asked me prior to the shoot if I knew about the XL1's "sound overload issues." I did some research, primarily using this newsgroup, and the Canon site, since I usually only work with DigiBeta, PAL format.

I ended up going from my 442 into the MA100 (I think that's what it's called) via XLR at mic level, and setting tone (nominal 0 on the 442) to -20 on the camera (mic level). Seemed to work fine for the interviews we did.

BUT...I had a very strange intermittent hum/buzz problem. Maybe someone can shed some light on it. It was not a power supply/ground loop problem. I was using isolation transformers, and A/B'd the set-up (both mine and the cameras) with and without AC power. The buzz did not diminish even with all pots on my mixer set at zero, i.e., no audio input. It was heard only in the camera audio return, not in my mixer. I also checked audio with my headphones plugged directly in the camera's headphone out, and the buzz was the same.

The noise modulated when someone walked in front of a camera.

We were shooting on a brightly lit sound stage in which the background was bright white (painted floor and walls).

An experienced cameraperson suggested that the buzz was being generated in the video itself -- too much "white" or too much contrast (or something) for the XL1s's electronics. And this seemed to be confirmed when the buzz changed as the operator adjusted the camera's iris. Could I have experienced some sort of bleed-through from overloaded video electronics? Any way around this?

The lighting was a combination of Kinoflows and other things, which of course, I had switched on and off to see if the buzz was lighting/dimmer-related.

Can anyone give me some guidance on this? I have another date with this set-up coming up shortly.

Thanks very much. I find this Prosumer stuff confusing....
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Old July 12th, 2003, 08:12 PM   #2
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I've heard of it happening with extreme video levels and also in scenes with fireworks. This is not limited to DV either. It can happen on almost any format, including Beta SP, not sure about DigiBeta. Light the scene more evenly and avoid over exposure.
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Old July 23rd, 2003, 12:55 PM   #3
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Audio "fuzz"

I've also noticed this problem when over-exposing the visual field of the camera. I agree with Jeff, that this can happen with extremely bright exposures, light levels and backgrounds. I was using some practicals in my garage to shoot against a Roscoe Blue painted wall and noticed the same thing. I had to diffuse the light a good bit and use some different full spectrum fluorescent lighting options to cure it.
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Old July 24th, 2003, 06:15 AM   #4
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It does appear that having portions of the image well into zebra can increase the audio noise floor by 3 dB. Using AC power can increase the noise floor a bit, say 1 dB. The MA-100 increases the noise floor about 3 dB but has 6 dB gain so the net may turn out to be a 3 dB improvement in overall S/N ratio.

Some quicjk tests: Using an XL1 with direct firewire feed to computer, 16-bit audio mode. Audio data viewed using CoolEdit Pro 2.1 analysis tools. List follows with the test conditions and average RMS noise level of the capture audio wave file for each test case reference to max possible digital record level. In all cases the input jack was open circuited (nothing connected)

-71 dB: XL1, Audio 1 input, MIC setting, AGC on, lens cap on, battery power

-60 dB: XL1, Audio 1, MIC setting. manual gain set to max, lens cap on, battery power

-57 dB: XL1, MA-100, Audio 1, manual gain set to max, lens cap on, battery power

-57 dB: XL1, MA-100, Audio 1, manual gain set to max, lens cap off, white scene, no part of image in zebra, battery power.

-54 dB: XL1, MA-100, Audio 1, manual gain set to max, lens cap off white scene with potions (5%) well into zebra, battery power

-56 dB: XL1, MA-100, Audio 1, manual gain set to max, lens cap off white scene no part of image in zebra, A/C power via CA-900.

The primary noise component in all cases was horizontal scan rate (15,750 kHz). Removing this noise using a notch filter improved the noise floor by about 1 dB. With the MA-100 attached a secondaty noise peak (singificantly lower than the 15750 noise peak) appeared at about 8 kHz
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