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What do GAIN controls on a Panasonic HDX900 actually do?


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#1 Bwana George

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Posted 01 September 2008 - 07:23 AM

After many years in film I am relatively new to the world of HD video. I'm shooting with a Panasonic HDX900. It has three settings for the gain control (low, medium, high). What "EXACTLY" does the gain control do, and what effect does each setting have?
Thanks.
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#2 Walter Graff

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Posted 01 September 2008 - 10:36 AM

Think of an audio amplifier. Want the music louder, you turn up the volume. Video gain is just that, a gain control for an amplifier in the video circuit. Think of film and how you can push and pull your exposure except film has much more logarithmic method than video and often more tolarable range. Like an audio amplifier, gain affects elements that might not be desirable outside of your signal. Just as an amplifier on a stereo can cause distortion, as you amplify the video signal, you create noise. Video cameras use terms such as 3db, 6 db, etc. So each is a logarithmic amplification of the last. But different manufacturers have different results in terms of how black and how clean a picture looks at 0 db for instance as each step of the gain control in their cameras is based on their formulas. So you can not simply say that 0 db on a Sony camera is the same as it is on a Panasonic camera. +3 on a Sony is often noiser than +3 on a Panasonic. Basically you want to shoot at a setting that is as noise free in the blacks as possible for normal exposure. You would understand the range of blacks and tolerences to noise with gain by setting a baseline on a waveform monitor and a chip chart to see what blacks and how many steps of black is accomplishable and what is desireable to your taste. And perhaps you want a bit of noise so you could shoot with the next gain setting. It's a matter of taste. Most people push video gain when there is less light and less exposure. You are affecting exposure index of video with the gain control albiet amplifying everything including elements of a picture that are less desireable, namely noise.
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