All the audio mixer circuit examples I see online are based off of the summing amplifier:
This is an inverting op amp configuration so the output is inverted. I built a similar circuit and I couldn't tell that the output signal was inverted by listening to the audio…so is there a reason why you would want to de-invert the output of the mixer, by putting in another inverting op amp stage at the output, like in this circuit:
If the audio output sounds the same whether the output signal is inverted or not, why would you ever need to de-invert the output?
Best Answer
When listening to a single channel, delay or inversion doesn't matter. When the overall audio has multiple signals (stereo has two, for example), then the relative phase or inversion between channels matters. You can invert all channels or none. Inverting some but not others messes up the phase relationship between the channels and the sound position you are supposed to perceive from them won't be correct.