What is the difference between analog and digital gain?

[hellboy80]

What is the difference between analog and digital gain?

[Marsu42]

What is the difference between analog and digital gain?

As a guideline, digital gain just moves data around the histogram which is fine for jpeg or video, but just loses dynamic range for raw. Also all cameras' highest isos are digital only, meaning for example on crop you should avoid anything above 3200. Read more here when digital iso can make sense (read noise vs. photon noise): http://magiclantern.wikia.com/wiki/ISO

[hellboy80]

Oh, sorry, I ment audio analog and digital gain...

[dmilligan]

There is no difference between what these mean for audio or what they mean for images. The same thing is happening, a physical phenomenon is converted into an electrical signal (voltage) then this signal is digitized, the only difference is the physical phenomenon that is being captured and the means by which it is converted into an electrical signal (i.e. a microphone diaphram vs. a photon sensel)

Analog gain is applied electrically by an amplifer circuit before the signal is converted into 1s and 0s by a ADC. Digital gain is just multiplication basically of the digitized value. This means you loose resolution. For example a digital gain of 2x (~3db) means all the values coming in are doubled, so certain values (the odd numbers in this case) are no longer possible, which means instead of capturing a 16 bit audio value, you're really only capturing a 15bit one.

[hellboy80]

Great explanation. Thanks!
BTW, the gain that my Canon 5DMII has (without ML) is analog or digital gain?

[dmilligan]

It's probably analog first, until it runs out of ability to increase it any more, then after that point it's digital IDK. This is how ISO works though, the "main" ISOs below 1600 (3200 on some nicer cameras) are analog gain applied to the elctrical signal, after that point the ISOs are digital gain (multiplcation) applied to the captured image. This is why you shouldn't use digital gain, you can just do it in post later (it's easy for a computer to multiply!), and you have precise control over it, so you're not loosing any data by potentially clipping (multiply large enough numbers together and your result will be greater than what can be stored in a specific number of bits, so it must be clipped to the maximum).

[1%]

I've found that on AK4646 the digital gain really pumps up the noise floor and makes you hear all of the background. Better off using something with gain/volume on it like a mixer/preamp and adjusting there after you run out of analog.