Thank you for the detailed responses. In case anybody interested, here are results:
My schematics is as following:
Details:
- I haven't use "gain" capacitor (marked as C2 on DimKo's schematics)
- I use R2=10K
- The actual problem with my readings was in a software, my readings were slow and I missed short sounds
- My circuit run without bypass capacitors on LM386 (because my target was to detect only loud sound), but I've tried adding them and they reduce noise from PWM and switching pins significally