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# DTMF Identification

The `audiopreproc` module can perform DTMF (Dual-Tone Multi-Frequency) dial tone detection and identification. In this mode, the module can accurately detect and identify tones corresponding to the numbers 0-9, the letters A-D, and the asterisk (*) and hash (#) keys.

To enable DTMF dial tone identification you can:

- set the `audiopreproc` mode to `A` to enable the output classification stream. In this case, by default the `DoToneClass` parameter is set to `Auto`, and Speech Server identifies DTMF tones for 8kHz (telephony) audio, but not for 16kHz audio. You can also set `DoToneClass` to `True` to always identify DTMF tones. Set `DoToneClass` to `False` to never identify DTMF tones.
- set the `audiopreproc` mode to `T` to output detected tones to a separate stream.

These options are not mutually exclusive.

For an example schema incorporating DTMF dial tone identification, see Identify DTMF Dial Tones. This schema produces a stream of DTMF labels (such as `<DTMF-1>`, `<DTMF-A>` or `<DTMF-#>`).

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