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How much is 3db of gain on a DVX100?


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#1 Sakari Suuronen

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Posted 10 February 2007 - 09:59 AM

I did a quick search but didn't find the answer, so in F stops, how much is 3db of gain and does it double when the gain is 6db and so on? Is there a simple formula calculating this? Do gain levels vary with different cameras, say DVX, HVX, XL2 or even the F900 or the Viper? Is 3 db of gain always the same amount in F stops?

Edited by Sakari Suuronen, 10 February 2007 - 10:00 AM.

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#2 Phil Rhodes

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Posted 10 February 2007 - 12:12 PM

Hi,

Gain of 6dB doubles the signal, and is thus equivalent of a one-stop increase.

Phil
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#3 Alessandro Machi

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Posted 10 February 2007 - 12:23 PM

Hi,

Gain of 6dB doubles the signal, and is thus equivalent of a one-stop increase.

Phil



Do you have a technical resource, are you the technical resource, is there a technical resource. I think that sounds about right by the way.
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#4 David Auner aac

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Posted 10 February 2007 - 04:14 PM

Do you have a technical resource, are you the technical resource, is there a technical resource. I think that sounds about right by the way.


Well I ain't no source, but I agree. 6db is one stop. Dunno were I read that though. Maybe some guy told me...

Cheers, Dave

Edited by David Auner, 10 February 2007 - 04:14 PM.

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#5 Alessandro Machi

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Posted 10 February 2007 - 05:06 PM

Well I ain't no source, but I agree. 6db is one stop. Dunno were I read that though. Maybe some guy told me...

Cheers, Dave


lol, I NEVER use automatic exposure when I shoot video so whenever I switch the gain on my camera, I've never actually noticed exactly how much the gain setting would change the f-stop reading. I'm glad to actually know the f-stop equivalent now. A Simple but useful topic question.

I've always been a fan of 6 DB versus 9 DB because it really doesn't add noticeable gain but that extra stop sure can make a difference in lower light situations.
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#6 Delorme Jean-Marie

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Posted 10 February 2007 - 08:04 PM

from my experience what ever db you put over zero will add noise so unless you are poor in lighting never ever add db's (for fiction) unless you want a noisy effect
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#7 Alessandro Machi

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Posted 10 February 2007 - 10:21 PM

from my experience what ever db you put over zero will add noise so unless you are poor in lighting never ever add db's (for fiction) unless you want a noisy effect


I seem to recall that I could get away with 6DB of gain and it really was hard to notice any additional noise. But if I'm shooting an interview, I would try to avoid using gain since the shot can be lit. There could be a lens quality trade off as well, especially with zoom lenses. Shooting with the f-stop wide open with no gain versus shooting at 6DB gain at lets say 2/3 of a stop from being wide open, one doubly benefits, slightly more exposure to the shot (assuming it was needed), plus the lens isn't wide open.

There have been times where I decided not to do gain and then found later that the camera actually didn't pick up subtle tones that were present. Those tones would have been picked up with 6DB gain. Other times, by using the 6db gain, I not only picked up all the nuances, but because I had also incorporated black stretch, I could recrush in post and get what looked to be the best of both worlds, additional information in the scene, plus no noticeable increase in grain.

I don't know if 6DB of gain is the same in a betacam sp camera versus a canon XL1, so if we're talking different cameras than there may not be a uniform standard.

Question...could a camera manufacturer, in an effort to make their gain look cleaner than the competition's cameras, choose to make the standard no gain setting be slightly less sensitive than it actually is capable of, aka a lower ASA, but then use the additional sensitivity that is actually there towards the gain settings. In essence, a 9 DB gain is really 6 DB, and the 6DB gain is actually 3DB.

From a marketing point of view, to have the cleanest 6DB gain around would be a great selling point.
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#8 Michael Nash

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Posted 10 February 2007 - 10:38 PM

There's no such thing as a "standard" of zero gain between different cameras and/or manufacturers. It's an arbitrary value set by the engineers who develop the camera, presumably to give the best optimum performance under optimum conditions. Zero db on one camera may match +6 db on another, and yield similar sensitivity and noise. Such is engineering -- marketing, is another story. ;)

In most cases, +6 db of gain will increase sensitivity by about one f-stop. But as there are lots of variables, don't expect it to be precise. But it is a useful rule of thumb.

While we're at it, reducing the "detail coring" or "crispening" (depending on camera manufacturer) can control the edge enhancement on noise artifacts when using boosted gain. The tradeoff is a loss of enhancement on fine detail, while still retaining enhancement on larger shapes.
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#9 Phil Rhodes

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Posted 11 February 2007 - 08:03 AM

Hi,

Panasonic cameras are widely held to be about 3dB less sensitive than eqivalent Sony gear, and quieter to boot. That said, Sony cameras often have a -3dB setting, so it's really up to the user. Yes, it's up to the manufacturer what they want to consider "normal" in terms of noise and sensitivity. Yes, this can be played for marketing reasons.

Phil
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#10 Alessandro Machi

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Posted 11 February 2007 - 01:19 PM

Hi,

Panasonic cameras are widely held to be about 3dB less sensitive than eqivalent Sony gear, and quieter to boot. That said, Sony cameras often have a -3dB setting, so it's really up to the user. Yes, it's up to the manufacturer what they want to consider "normal" in terms of noise and sensitivity. Yes, this can be played for marketing reasons.

Phil


Funny you mention that. I remember a long time ago looking at a Panasonic 300CLE (I think that is what it was called), and I was surprised at how clean the first gain setting seemed to be. If their default non gain setting is slightly slower, by design, then that would mean that their first stage gain setting would look cleaner than the competitions. On the other hand, losing that slight bit of sensitivity on the non gain setting could prove annoying because it could require one to use the first stage gain more than necessary.
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