Adjusting advanced options for machine detection

This article describes how to adjust the Voice Device Engine advanced options for machine detection.

Phone Engine Advanced Options Background

If your system is operating in another type of environment (such as behind a PBX), you can customize the cadence detection algorithm to suit your system through the adjustment of the cadence detection parameters.

Cadence detection analyzes the audio signal on the line to detect a repeating pattern of sound and silence, such as the pattern produced by a ringback or a busy signal. These patterns are called audio cadences. Once a cadence has been established, it can be classified as a single ring, a double ring, or a busy signal by comparing the periods of sound and silence to established parameters.

Note: sound is referred to as "nonsilence".

You can cause cadence detection to measure the length of the salutation when the phone is answered. The salutation is the greeting when a person answers the phone, or an announcement when an answering machine or computer answers the phone. By examining the length of the greeting or salutation you receive when the phone is answered, you may be able to distinguish between an answer at home, at a business, or by an answering machine.

By examining the length of the salutation, you can estimate the kind of answer that was received. Normally, a person at home will answer the phone with a brief salutation that lasts about 1 second, such as "Hello" or "Smith Residence." A business will usually answer the phone with a longer greeting that lasts from 1.5 to 3 seconds, such as "Good afternoon, XYZ Company Inc." An answering machine or computer will usually play an extended message that lasts more than 3 or 4 seconds. However, for the following reasons this method is not 100% accurate:

  • The length of the salutation can vary greatly.
  • A pause in the middle of the salutation can cause a premature connect event.
  • If the phone is picked up in the middle of a ringback, the ringback tone may be considered part of the salutation, making the length of the detected salutation inaccurate.

In the latter case, if someone answers the phone in the middle of a ring and quickly says "Hello", the nonsilence of the ring will be indistinguishable from the nonsilence of voice that immediately follows, and the length of the detected salutation may include both the partial ring and the voice. The salutation would appear to be the same as when someone answers the phone after a full ring and says two words.

Because a greeting might consist of several words, call progress analysis waits for a specified period of silence before assuming the salutation is finished. The Required Prompt Silence parameter determines when the end of the salutation occurs. This parameter specifies the maximum amount of silence allowed in a salutation before it is determined to be the end of the salutation. The Maximum Answer parameter determines the maximum allowable answer size before returning a connect. The Low 2 Ring Minimum parameter is used for classifying a double ring cadence.

The following points summarize these settings and their default values:

  • Required Prompt Silence: the maximum silence period allowed between words in a salutation; default is 1500 milliseconds.
  • Maximum Answer: the maximum allowable length of answer size. When detected salutation length exceeds this value, a connect is returned to the application; default is 10,000 milliseconds.
  • Low 2 Ring Minimum: Minimum long low duration of double ring. This should be used in areas such as the United Kingdom for double rings on the ringback tone; default is 2250 milliseconds.

Cadence detection waits for the end of the salutation before returning a connect. The end of the salutation occurs when the salutation contains a period of silence that exceeds Required Prompt Silence or the total length of the salutation exceeds Maximum Answer.


Long Salutation

In cases of unusually long answering machine salutations, the message left on the answering machine is missing the initial part of the message.
The cause is that the salutation exceeds the Maximum Answer time, at which time the message starts to be delivered although the answering machine is not yet in recording mode. Increasing the Maximum Answer time will correct the problem; as an alternative, decrease the length of the user's greeting.

Long Pause in Greeting

In rare cases the answering machine salutation contains an embedded long pause (e.g., when a company greeting is followed by a person's self-recorded name). When the long pause is encountered, two situations may result:

  • The salutation before the pause is short enough to be misinterpreted as a human answering the phone.
  • The message is starting to be delivered prematurely, as in the previous example.

To correct the problem, increase the Required Prompt Silence. Note that the silence time also affects the pause after a salutation is ended and the notification has started. Also, making the Required Prompt Silence too long may cause a real person being called to believe that there is nobody on the call, causing them to hang up prematurely.

Noisy Background

Significant background noise may make it difficult to distinguish between silence and nonsilence (e.g., a mobile phone call answered by someone in a noisy public environment). The symptom is that although a human answered the phone, the system thinks it is an answering machine because the Maximum Answer time is exceeded. One solution that has been implemented successfully is to modify the callout script so that in the case of answering machine detect, the recipient is asked to push any key on the phone pad. If a key is detected during a short period of time it is assumed that a human answered; otherwise it is treated as an answering machine.

Playing Music instead of ringing

Many mobile phones allow the user to change the default ringing to play music. This means that the caller hears music rather than the usual ringing sound. As a consequence, the system does not detect ring tones and the call is not considered successfully placed. The only solution is to set the phone to ring normally for caller rather than playing music.

Further Information

xMatters References: SUP-3605, DOC-2130, JDN-1205; originally created by Don Clark

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