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 it this way once: I used floats (samples between -1 and 1), and I initialized a "autoGain" variable with a value of 1. Then I would add all the samples together (could also be more than 2). Then I would multiply the outgoing signal with autoGain. If the absolute value of the sum of the signals before multiplication would be higher than 1, I would make assign 1/this sum value. This would effectively make autogain smaller than 1 let's say 0.7 and would be equivalent to some operator quickly turning down the main volume as soon as he sees that the overall sound is getting too loud. Then I would over an adjustable period of time add to the autogain until it finally would be back at "1" (our operator has recovered from shock and is slowly cranking up the volume :-)).