On muffwiggler Harry Bissell suggested to use a full wave rectifier as an input stage to his envelope follower. When contemplating to try this I thought: but then the signal is rectified by this new input stage AND the 1st op-amp in the peak detector. This makes it possible to maybe simplify the original design by leaving out the rectifying op-amp stages of the peak detectors. I tried this on a bread board and it works nicely. So this saves 3 opamps and produces the same results. I pimped the signal a bit by adding some gain to the output stages of the peak detectors. The signal processing part of the schematic can thus be reduced to:
Which results in the same envelope as the initial approach.
Note: the picture shows the envelope when I was experimenting with 1 simplified peak detector (the others were not connected) so the end result could be smoother.
To make the schematic complete you have to add the 40106 and 4017 circuit as shown in the original schematic.