Amplifier/rectifier/filters advice needed

Using Arduino Audio
1

I'm looking for circuit to amplify and feed signal from electret mic to ADC. My goal is to detect is sound level is above some threshold to detect quite loud screams.

I've found two amplifier circuits:

First on the one BC337 from here: Cheap Sound Sensor for AVR – tinkerlog

Ant the second on LM386 (audio amplifier\op-amp) from here: DIY Tengu on a breadboard – tinkerlog

I've found great schematics here in forum: Audio Input - #3 by CrossRoads - Audio - Arduino Forum unfortunatelly without values for components.

Before building I'd like to ask some questions:

  • It seems that negative part of waveform will be feeded into ADC with transistor circuit?
  • Does circuit with LM386 have shift in output so values will be always positive (in code he subscract 512 so I assume it have bias)?
  • Can I place envelope detector (Envelope detector - Wikipedia) after LM386 circuit, how to calculate values?
  • Can I use the same circuit with line-level audio signals?

Thanks in advance!

2

Here is a one-transistor amplifier from the Playground: http://www.dtic.upf.edu/~jlozano/interfaces/microphone.html

This example, also from the Playground, use an IC amplifier: http://didier.longueville.free.fr/arduinoos/?p=1057

3

Thanks for the response, both circuits from your links seems to come without biasing and envelope filter, is it good for ADC?

Thanks!