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Answering Machine Detection (AMD)

The Answering Machine Detection (AMD) feature can be enabled on outbound calls to provide an indication of whether a call has been answered by a person or a machine. To use this feature, provide the amd property in a dial verb.

In this example, the Answering Machine Detection feature is activated as soon as the call is answered, and later sends a webhook to amd to determine if a human or a machine has answered the call.

  "verb": "dial",
  "actionHook": "dial",
  "callerId": "+49XXXXXXXXXXX",
  "target": [
      "type": "phone",
      "number": "+49XXXXXXXXXXX",
      "trunk": "Twilio"
  "amd": {
        "actionHook": "amd",
        "recognizer": {
            "vendor": "microsoft",
            "language": "en-US",

Example of a webhook payload:


{"type":"amd_machine_detected","reason":"hint","hint":"call has been forwarded","language":"en-us"}



The full set of configuration parameters:

Parameter Description Required
actionHook A webhook to receive an HTTP POST for AMD events. Default is amd Yes
thresholdWordCount The number of spoken words in a greeting that result in an amd_machine_detected result. The default value is 9. No
recognizer Speech recognition parameters, used as per the gather and transcribe functions. The default value is application. No
timers An object containing various timeouts. No
timers.noSpeechTimeoutMs The time in milliseconds to wait for speech before returning amd_no_speech_detected. The default value is 5000. No
timers.decisionTimeoutMs The time in milliseconds to wait before returning amd_decision_timeout. The default value is 15000. No
timers.toneTimeoutMs The time in milliseconds to wait to hear a tone. The default value is 20000. No
timers.greetingCompletionTimeoutMs The silence in milliseconds to wait for during greeting before returning amd_machine_stopped_speaking. The default value is 2000. No


The payload included in the actionHook always contains a type property describing the event type. Some event types may include additional properties.

Event Description Additional Properties
amd_human_detected A human is speaking. {reason, greeting, language}, where:
- reason โ€” a short greeting,
- greeting โ€” a recognized greeting.
- language โ€” a recognized language.
amd_machine_detected A machine is speaking. {reason, hint, transcript, language}, where:
- reason โ€” a hint or long greeting.
- hint โ€” a recognized hint.
- transcript โ€” a recognized greeting.
- language โ€” a recognized language.
amd_no_speech_detected No speech was detected. -
amd_decision_timeout No decision was able to be made in the time given. -
amd_machine_stopped_speaking Machine has completed the greeting. -
amd_tone_detected A beep was detected. -
amd_error An error has occurred. An error message.
amd_stopped Answering Machine Detection was stopped. -

Multiple events can occur during a single call. For example, on a call to an answering machine, the sequence could be:

  1. amd_machine_detected
  2. amd_tone_detected
  3. amd_machine_stopped_speaking

Inbound calls

You can use Answering Machine Detection for incoming calls by adding an amd property in a config verb. It can be useful in situations where Voice Gateway is located behind a dialer. In these cases, the dialer initiates the outbound call and then links it to Voice Gateway via an INVITE request.