Touch Tones or DTMF
From TeleFlow
Touch tones, or DTMF, are sounds that are created using telephone keypad, or other means, to send information through automated systems.
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DTMF
DTMF standards for "Dual-Tone Multi-Frequency", and are the audio signals that are generated when you press the buttons on a touch-tone telephone. They can be created by nearly active telecommunications development environments in order to interface with other automated telecommunications services. DTMF describes numbers (0,1,2,3,4,5,6,7,8,9) symbols and letters (*, #, A, B, C, D).
Issues with DTMF
Talk-Off
Talk-Off, or Talkoff, is the term that describes when a human voice is able to trigger touch tones, or DTMF tones during a telephone call. Talk-Off occurs when a signal processing system tries to translate sounds into to touch tones. Some people's voices are able to recreate touch tones frequently relative to the general population.
Human Voice as DTMF
Talk-Off is possible as human voices speak in the same frequencies as DTMF combinations. Unlike real touch tones generated using telephone keypads, human-voice created touch tones are not sustainable and can generally be isolated by algorithms created to determine true DTMF. However, occasionally a speech signal will momentarily contain strong frequencies in just the right frequency bands which then occur as DTMF sounds.
Testing for Talk-Off
Algorithms to detect talk-off include testing for frequency limits, signal-to-noise ratios, and duration. Hardware manufacturers attempt to strike a balance talk-off and required touch tone durations. Talk-off could be eliminated, but the result would be having to hold down telephone buttons for very long durations in order to register DTMF. Generally, it is expected that talk-off will occur from time to time, so when hardware and driver software is developed for the market, it is tested against recordings made available by Mitel and Bellcore to ensure functionality within acceptable parameters.
How to Manage Issues Surrounding Talk-Off
On occasion, talk-off can become a problem for an installed system. The immediate impulse to fix is the issue is to lengthen the touch tone detection duration in order to reduce the instances. This will only result in frustration of the majority of other users when their touch tones are not recognized. We therefore do not advocate this approach, as the manufacturers of the voice hardware have exhaustively determined the sweet-spot for you.
If the problem is frequent and system wide, ensure telephone and other cables are properly insulated from other equipment as their is a potential for them to become radio antennas. This is very rare and very probably only related to analog equipment.
Application Wide
Primarily, you should ensure your system is capable of handling all touch tones including A,B,C,D. In TeleFlow, this is handled with the "Others" path. Generally a search for Get-TT and Dictation steps, and then reviewing the application for what-if scenarios should be enough to ensure talk-off will not cause too many issues.
Please note that the TeleFlow software comes with pre-generated touch tone wave files for your use. The Generate Touch Tone step can also create any touch tone included A,B,C and D.
Specific Users
For the occasion where a user is having problems and complaining of breaks or sudden losses of information, the best approach is to explain to that person that modern equipment uses compression which can sometimes cause certain voices to trigger touch tones. Work with them to tune the system by requesting the date and time the problem occurred. You can then review the TeleFlow logs to determine what the result of the talk-off was and amend it.
