Asterisk Answering Machine Detection

I need someone experienced with Asterisk to create a good solution to detect answering machines. Automated calls are placed out via the dialplan. If it detects a voicemail, it should hang up. The problem with the existing AMD function is that it's very inaccurate so I need something custom made, preferably to detect the following: - Talking within less than a second of answering phone - Talking for more than 4 seconds after answering phone