Answering Machine Detection

AMD (Answering Machine Detection) is the technology that analyzes the audio at the start of an answered outbound call to determine whether a live person or an answering machine/voicemail picked up. When AMD identifies a machine, VICIdial can automatically hang up, leave a pre-recorded message, or route the call differently — preventing agents from wasting time listening to voicemail greetings.

How It Works in VICIdial

VICIdial supports multiple AMD methods configured through the amd_type setting. The primary methods are Asterisk’s built-in AMD application and CPD (Call Progress Detection). Both analyze the initial audio after the call connects — measuring the length of the first utterance, pauses between words, and total greeting duration to classify the answer as HUMAN or MACHINE.

When AMD detects an answering machine, the amd_send_to_vmx setting determines the action: hang up, play a voicemail drop message, or route to an extension. When a live person is detected, the call is immediately routed to an available agent. The AMD agent route options control how calls classified by AMD are delivered to agents.

AMD adds a brief delay (typically 1-3 seconds) to call connection while the system analyzes the audio. This creates a short pause before the live person hears the agent, which some leads perceive negatively. The accuracy/speed trade-off is configurable through AMD sensitivity parameters.

Why It Matters

In outbound campaigns, 30-60% of answered calls may reach voicemail. Without AMD, agents spend significant time listening to greetings before recognizing a machine and hanging up, dramatically reducing calls per hour and agent utilization. AMD can reclaim this wasted time and increase productive talk time by 20-40%.

However, AMD is imperfect. False positives (classifying a live person as a machine) result in hung-up leads who were ready to speak. False negatives (classifying a machine as human) waste agent time. Tuning AMD sensitivity to balance these errors is critical. See our VICIdial AMD guide and AMD optimization feature page for tuning strategies.