AMD (Answering Machine Detection)
Asterisk logic that decides whether an answered call is a live human or a machine.
Answering Machine Detection (AMD) is Asterisk logic that listens to the opening moments of an answered call and classifies it as a live human or a machine. VICIdial uses it so agents are not handed voicemail greetings.
How it decides
AMD works on speech rhythm, not content. It measures the length of the initial greeting and the silence around it: a person says "hello" and stops, an answering machine plays a longer uninterrupted announcement. Asterisk's AMD application exposes those thresholds - total analysis time, greeting length, word and silence durations - and VICIdial calls it from the dial plan through VD_amd.agi.
Because it is a timing heuristic, it is never exact. Two failure modes matter:
- False machine - a talkative person is classified as a machine and hung up on. This is the expensive one: it burns a good lead and, if the person answered live, the regulator counts that call the same way it counts any other abandoned call.
- False human - a machine is passed to an agent, who listens to a greeting and dispositions it.
The campaign settings
amd_send_to_vmx on the campaign decides what happens once AMD says "machine": N connects the call anyway, Y hands it to the voicemail-message extension so a pre-recorded message can be left. The message extension itself is am_message_exten, which ships pointing at Asterisk's vm-goodbye prompt until you replace it with your own audio.
Systems with call-progress detection hardware or software have a second lever, cpd_amd_action, which routes a detected machine to DISPO, MESSAGE, CALLMENU or an INGROUP rather than simply hanging up.
Tuning it
Longer analysis means more accurate classification and a longer pause before a real human hears an agent - the "dialer silence" customers complain about. Shorter analysis transfers faster and misclassifies more. Tune it with recordings in front of you: pull a sample of calls dispositioned as machine and listen for humans in the set. If you find them, lengthen the analysis window before touching anything else.