I was hoping it was going to be a simple addition of a POT or something!!
Hi,
The implication from the diagram is that you need to control four channels, but four-gang pots are not particularly available, nor cheap! Also note the reference to a "Log" pot to achieve a
subjectvely linear volume characteristic.
Do you also want/need "Balance" (Left/Right) and/or "Fade" (Front/Back) controls? If so, there are probably many dedicated/custom ics which can do the job.
However, if you want to Do It Yourself "on the cheap", then an audio attenuator can be made with "variable resistors" of various types, such as MOSFETs or Light-Dependent-Resistors. My first remote-controlled "Quadraphonic" audio controller used 4 torch bulbs (before the days of LEDs) illuminating 4 LDRs (to give the above-mentioned Volume, Balance and Fade controls).
Cheers, Alan.