Algorithm to mix sound

Question

I have two raw sound streams that I need to add together. For the purposes of this question, we can assume they are the same bitrate and bit depth (say 16 bit sample, 44.1k

Answer 1

I did the following thing:

MAX_VAL = Full 8 or 16 or whatever value
dst_val = your base audio sample
src_val = sample to add to base

Res = (((MAX_VAL - dst_val) * src_val) / MAX_VAL) + dst_val

Multiply the left headroom of src by the MAX_VAL normalized destination value and add it. It will never clip, never be less loud and sound absolutely natural.

Example:

250.5882 = (((255 - 180) * 240) / 255) + 180

And this sounds good :)