I first assumed it would be as simple as wiring two outputs to one input (in fact, I've done this before... so I know it can work fine in some situations). However more recently, a conversation with a friend and some research has revealed to me that it's not a good idea because combining audio signals can be unpredictable, possibly sound poor, and be potentially damaging to the source circuits.
The first thing I want to know is: why exactly?
I thought two waveforms would be combined in the sense that the amplitude of each signal would just be added together at any given point along the waveform. How I understand the problem now is that if one of the outputs is a good amount higher voltage than the other, it can "seep backward" into -and overload- the other output's circuits. (I'd like to better understand how/why this occurs)
The other main thing I want to know is: how do I solve this?
I'd like to make a simple mixer circuit such as one of these.
Have my computer, TV, and a CD player (or iPod) all connect to one set of speakers and sub. (not necessarily all sending a signal at once, but perhaps two simultaneously (and maybe all 3 if my computer decides to make a system noise))
Combine the audio from my XBox 360 mic with an audio source (computer/ipod/ect.), and have them both go to the mic input on the controller. Thus playing background music or whatever else over XBox Live chat.
Though reading that page rose more questions, such as:
Should I know the load impedances of my sources as well as the device accepting the new signal, and how how they compare to the resistor values in the schematic (so to find what optimal values they should have, and not introduce noise or lose some of the signal)?
Does attenuation simply mean the same thing as signal loss (I'm guessing beginning at low amplitudes of the waveform)?
Should I definitely go for the active stages (circuit 2 and higher), or will a passive mixer work just fine (circuit 1)? (I'm not completely sure what is meant by "Suffers with the problem of no buffering and possible missmatches and losses.")
What does "Op-Amp" refer to, and what's meant by "busses" and "sends"?
Should I bother with the 27p and 47p caps?
Help or answers to any of these questions would be very appreciated. Thank you.