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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old March 19th, 2007, 09:10 PM   #1
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Gain settigns on A1..curious`

i just had a look at the firmware wishlist poll, and i noticed the gain vlaue request of 9 and 15..

im curious doesnt the A1 have a 9db option?

I know on DVX camp thres 3, 6, 9, 12, 18... 18 is unusable, 12 is ok, but noisy 9 is virtually indistringuishable as are the other 2..

Just wondering, what are the gain settings for the A1? does anyone have any samples?
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Old March 19th, 2007, 09:52 PM   #2
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Gain settings available for XH-A1 are:
-3, 0, 3, 6, 12, 18, 36 dB ...

Possibly people are chasing an intermediate setting?

I have not used any greater then 6dB

Cheers, Robert
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Old March 20th, 2007, 04:14 AM   #3
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For people in the special event industry where they don't have much if any control, 6dB may not be enough for certain situations... 12dB is too much & adds too much noise. 9 dB may just be the right go-between with no adding as much noise as with the 12dB setting.

I've never owned a camera that didn't have 3dB gain increments for at least the low to mid range scale.

Bill
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Old March 20th, 2007, 11:00 AM   #4
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Way back in the day when I was considered an "audiophile" (is that term even used anymore?), I was taught that to hear any decernible difference in level change, be it volume, tonality, etc., there had to be at least a 3dB increase or decrease. That magic number always stuck in my head & I always figured it was the same for video.

With the A1's jump from +6 to +12, it forces those that just need that little bit of a noticeable push to +9 for those god awful low light situations in the special event industry, to jump 2x that. I still say that the larger increments should be for the mid to upper end of the scale.

Surely this can be implemented in firmware... but then, what do I know? :D

Bill
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Old March 21st, 2007, 05:03 PM   #5
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3 dB is also a logical unit in audio and video because it represents a doubling in amplitude and exposure, respectively. And that doubling in exposure is of course also a full stop.
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Old March 21st, 2007, 07:32 PM   #6
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I thought 6 dB of gain equals one stop, i.e., doubling the amount of light reaching the imaging plane.
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Old March 22nd, 2007, 03:49 AM   #7
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If that's true I stand corrected. Mathematically 3db is approx. the equivalent of a factor 2, but maybe I'm missing something here?
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Old March 22nd, 2007, 09:26 AM   #8
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3 dB is a doubling of power or energy, not voltage. 6 dB is a doubling of voltage, and with a constant impedance, will result in a doubling of current (E=IxR) for a 4-fold increase in power.

In the case of video gain we are measuring voltage from the CCD, it is not a power measurement. Photons (light) hit the CCD and deposit charge that builds a voltage in each CCD pixel that is read at the end of the exposure period.

To test it your self, set up a static scene, in, say shutter priority auto exposure mode. Monitor the gain, aperture and shutter. Adjust the gain and watch the aperture change.
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Old March 22nd, 2007, 10:05 AM   #9
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Yes, 6dB gain change is 1 stop.

Though it's only speculation, intermediate gain settings may not be available if signal amplifier configuration is fixed in XH cams, but who of us mortals would know that... 6, 12, 18dB are the standard, but I wouldn't mind 9dB added.
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