I need to find a simple (preferably passive) way to take a stereo consumer line-level output, mix it to mono, and reduce it by 40dB to be used in a microphone level.
Following this answer: https://electronics.stackexchange.com/a/14982/1554 I see it's easy to use a pair of resistors to get down the levels I need. I've also stumbled across this schematic for mixing the two channels together:
I can't help but notice how similar these two schematics are, and am wondering if I could combine them. Minimizing parts and size is important to me, as I would like to build the whole thing inside an XLR plug. What values of resistors do I need in this stereo-to-mono schematic to also bring the levels down by ~40dB? And, how is that calculated?