Here's the idea, to wire up an R2R network, followed by an inverting op-amp stage. There's some resistor in the feedback loop and a resistor between the R2R and the inverting input. The gain of the op-amp is fixed and effectively I control the loudness of the audio signal by how much I attenuate the input signal to the resistor of the inverting input using the R2R network.
I thought to feed the audio signal into the R2R resistors, the more resistors that get fed the signal the stronger the signal will be. However I am not sure what to feed a resistor that I don't want to get signal? Short it to GND? DC? What else?