Depends on the maker, but most have a bad habit of using polarized tants in the audio path. The rest used 0.1uF or less non-polar, but then people complained of tinny sounding audio as no one bothered to do a R/C filter analysis.
But you have a chicken and egg situation, is it the controllers fault or the radios? Not all radios have bias and not all controllers charge caps backwards. You can solve the problem by removing the mic bias resistor from the radio, installing a non-polar cap anywhere in the audio path or replacing the polar cap with a non-polar. I used to use 10uF tants for audio but now everything I design uses 1uF 50V Ceramic because of this exact problem. Take a look at the schematic I posted earlier, it will suit your needs but I do not program that well, hence the open source of the hardware. If there is any intrest I will finish the PCB, which will measure 1.9" X 2.5" and about 0.5" tall and doesn't use any surface mount components.
