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 cannot believe that nobody knows the correct answer. Everyone is close enough but still, a pure philosophy. The nearest, i.e. the best was: (s1 + s2) -(s1 * s2). It's excelent approach, especially for MCUs.

So, the algorithm goes:

1. Find out the volume in which you want the output sound to be. It can be the average or maxima of one of the signals.
   factor = average(s1) You assume that both signals are already OK, not overflowing the 32767.0
2. Normalize both signals with this factor:
   s1 = (s1/max(s1))*factor
s2 = (s2/max(s2))*factor
3. Add them together and normalize the result with the same factor
   output = ((s1+s2)/max(s1+s2))*factor

Note that after the step 1. you don't really need to turn back to integers, you may work with floats in -1.0 to 1.0 interval and apply the return to integers at the end with the previously chosen power factor. I hope I didn't mistake now, cause I'm in a hurry.