Audio Envelope Follower for Arduino

Ok. One more try...

After reading many resources on Op Amps and various configurations, I decided to break down the project into three different functions.

1. Audio Processing - Removing the negative half of the audio input. I did this by using a summing op amp amplifier configuration. A voltage divider sets the offset and adds to the audio through a resistor network. Hence, there isn't any negative component into the op amp. I tried to do all amplification in this stage, but lost some accuracy further down the line. Hence, in this stage, I've just configured a gain of 2.
2. Envelope Follower - Not much to say here. It's just a direct implementation of an envelope follower circuit.
3. Final Amplification - This stage takes the output of the envelope follower and amplifies it to the full scale of the op amp. An LT1013 on a 5V supply can amplify up to about 4.4V.

The schematic is below. By adjusting resistor values, a different audio source can be used (R6,R7) or a different op amp (R1, R2).


Below are the simulation plots.
First is the audio signal, at ±1.2V.
Following that, is the op amp inverting input, from a tad below 0V (well within a diode drop of the rails) to +1.2V.
The next plot is the audio signal out. from 0V to 2.4V. The first op amp is configured for a gain of 2.
The next line is the output of the envelope follower,
followed by the output of the last stage of amplification. Note the plot scale. This is what I and others have been looking for.


I believe, unless you guys find something drastically wrong or make an amazing observation, that this will be final version.

Thanks for everyone's help, with a special shout out to @Audioguru