ffmpeg volume parameter format

Question

ffmpeg's -vol parameter is confusing me.

256 => normal (i guess meaning same as input volume, no change)
512 => (double the volume - read this somewhere).

So what to do for 3 times the volume? 1.5 times the volume?

Basically, lets say I have the max sound amplitudes (audacity levels) in 3 files as:

0.8
0.6
0.9

I want to amplify in the first two files, so that max=0.9 in all files. What parameters of -vol I would use?

Answer 1

Well, this is really elementary school maths, I suppose.

If 256 is norm (0.8), then you simply have to divide it by normative level and multiply with required level, e.g.

256 * 0.9/0.8 = 288
256 * 0.9/0.6 = 384

See cross multiplication.

The real question is, how to make ffmpeg output all audio normalized to 1, regardless of current amplitude level.