Envelope detector RC values
If you have a large ratio between the highest frequency of the information, and the carrier frequency, then you might set the RC time constant at the geometric_mean midpoint between the carrier period and the information period
Thus with 1MHz carrier (AM radio) and 5MHz voice/music, thus 1uSec and 200uSec, set the RC at sqrt(1uS * 200uS) = about 15uS.
===================================
By using the geometric_mean, you have a starting point of optimization.
There will be deterministic trash on output of the RC LPF. You may want to further filter the waveform.
You may need to perform some time simulations, with diode half-wave rectifiers, and think about the residual ripple coming from the RC LPF.