I was playing around with some computer code to process some audio. As part of it, I needed to combine the audio from two different sources. Everything is in raw, uncompressed, 16-bit signed samples, at 48kHz sample rate. So now I'm thinking, do I add voltage, or add power? The sample values are voltage (or so I've believed over the years). But in real life, adding a 2nd audio source just adds more power. If I have a 25-watt source, and another 25-watt source that might happen to be exactly the same audio waveform, combining them is going to get 50 watts, not 100 watts. But if I do this in voltage signals, what would be a 25-watt output would become a 100 watt output (assuming a sound system with sufficient capacity to not overload, and digital bits that won't overflow). So what's the proper way to combine two audio sources, in digital space, that correctly behaves like real life space where adding 25 watts and 25 watts gets you no free power?