A Simple 12 db low pass filter, use 2 BC547 NPN transistor and a stereo 100k pot for the cutoff, instead of the pot.
It’s possible to use 2 photo resistor. This filter is calibrated for 5v use, but also 9\12 volt for simple application.
I’ve developed it with Peppo at LEP lab. In Milano.
I use it in this 6 bit noise generator, video.
Val Pastel, made this filter audio test listen.