Gain settigns on A1..curious` at DVinfo.net

Peter Jefferson · March 19th, 2007, 08:10 PM

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?

Robert Garvey · March 19th, 2007, 08:52 PM

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

Bill Busby · March 20th, 2007, 03:14 AM

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

Bill Busby · March 20th, 2007, 10:00 AM

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

Steven Fokkinga · March 21st, 2007, 04:03 PM

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.

Don Palomaki · March 21st, 2007, 06:32 PM

I thought 6 dB of gain equals one stop, i.e., doubling the amount of light reaching the imaging plane.

Steven Fokkinga · March 22nd, 2007, 02:49 AM

If that's true I stand corrected. Mathematically 3db is approx. the equivalent of a factor 2, but maybe I'm missing something here?

Don Palomaki · March 22nd, 2007, 08:26 AM

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.

Bogdan Tyburczy · March 22nd, 2007, 09:05 AM

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.

March 19th, 2007, 08:10 PM	#1
Peter Jefferson Inner Circle Join Date: Apr 2003 Location: Aus Posts: 3,884	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?

March 19th, 2007, 08:52 PM	#2
Robert Garvey Regular Crew Join Date: Feb 2007 Location: Western Australia Posts: 100	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 __________________ Robert Garvey Photographer www.garvey.com.au

March 21st, 2007, 06:32 PM	#6
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,489	I thought 6 dB of gain equals one stop, i.e., doubling the amount of light reaching the imaging plane. __________________ dpalomaki@dspalomaki.com

March 22nd, 2007, 08:26 AM	#8
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,489	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. __________________ dpalomaki@dspalomaki.com

March 20th, 2007, 03:14 AM	#3
Bill Busby Major Player Join Date: Dec 2006 Location: Los Angeles, CA Posts: 959	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

March 20th, 2007, 10:00 AM	#4
Bill Busby Major Player Join Date: Dec 2006 Location: Los Angeles, CA Posts: 959	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

March 21st, 2007, 04:03 PM	#5
Steven Fokkinga Major Player Join Date: May 2004 Location: The Netherlands Posts: 204	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.

March 22nd, 2007, 02:49 AM	#7
Steven Fokkinga Major Player Join Date: May 2004 Location: The Netherlands Posts: 204	If that's true I stand corrected. Mathematically 3db is approx. the equivalent of a factor 2, but maybe I'm missing something here?

March 22nd, 2007, 09:05 AM	#9
Bogdan Tyburczy Regular Crew Join Date: Oct 2006 Location: Brooklyn Posts: 161	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.