Answering Machine Detection (AMD) - need to know Accuracy

Hello all,

I am using AMD for the human voice detection in my asterisk server…but i am unable to acheive full result when using Answering machine detection .
The scenario i am using is,only if the human attends the call,the calls getting in to the server server otherwise it will wait(queue) for the calls to attend in the server…it will not detect ivr voice and the hold music while waiting in call…
I am succeed in the above scenario but it takes 15-20 seconds after attending the call and detect human voice to enter the server…please help me to acheive the accuracy in AMD in asterisk