Noise is not caused by a certain ISO setting. High ISO isn't really what causes increased noise. The lower amount of light we usually allow into the camera when using higher ISO is what causes noise. If you limit the light to the same level at ISO 100 that you would use to properly expose for, say ISO 3200, and then try to boost those almost black shadows by five stops in post, you'll see the same thing as using ISO 3200 with the same exposure time (Tv) and aperture (Av) when shooting. If you're using an older camera, underexposing five stops at ISO 100 and then boosting by five stops digitally in post will result in more noise than shooting at ISO 3200 would. You'll also have more quantization errors.

For more, please see:

Why would using higher ISO and faster shutter speed yield more noise than using lower ISO and slower shutter speed?

Should higher ISOs really be preferred (all other things being equal)?

Regardless of whether you are shooting still images or video, if you want to decrease the amount of noise in a shot you need to increase the amount of light you're letting into the camera. The options you have for doing this are:

• Use a wider aperture
• Use a longer exposure time
• Add light to the scene