Voicemail Detection Settings That Actually Work

Recommended Baselines

• Greeting length threshold: 1.6–2.4s (longer → voicemail likelihood)
• Beep detection: enable with 500–1200Hz band emphasis and -28dB threshold
• Silence window: 600–900ms before first agent utterance
• DTMF presence: deprioritize voicemail if early DTMF detected
• Twilio AMD: use DetectMessageEnd with 2.0s max greeting

Hybrid Heuristic

// Pseudocode combining AMD + custom VAD/beep
const decision = (amd, vad, beep, dtmf, tGreeting) => {
  if (beep.detected && tGreeting > 1.7) return 'VOICEMAIL';
  if (amd.result === 'MACHINE' && vad.noHumanSpeech && tGreeting > 1.8) return 'VOICEMAIL';
  if (dtmf.early) return 'HUMAN';
  if (vad.humanSpeechStart < 1200) return 'HUMAN';
  return amd.result === 'MACHINE' ? 'VOICEMAIL' : 'HUMAN';
};

QA Checklist

• Measure FP/FN rates against 100+ labeled calls; track per-carrier
• Record features (greeting length, beep time, VAD events) for audits
• A/B AMD settings monthly; carriers change cadence
• Fail-safe: if uncertain → short intro + re-check before full pitch

Good / Bad / Ugly

• Good: Beep detection + AMD + VAD fusion; measurable thresholds.
• Bad: Relying on one signal (AMD only) → drift over time.
• Ugly: Double beeps, carrier ringback fakeouts; use cooldown + retry strategy.