Echo allows manual obfuscation of calls using a DTMF key sequence entered by the user into their handset.  When the system detects a user pressing a specific sequence of digits, the obfuscation begins, and any audio will be immediately and irreversibly overwritten with the tone specified in the /audio/obfuscation/tones/ section of the settings.xml file. To stop obfuscation, the stop key sequence must be entered, whereupon the audio will be written normally to the call's stream.

The start and stop key sequences can be defined in the settings.xml file located in {app}\ProgramData\Tri-Line\Echo, using the dtmfStart and dtmfStop elements. The following settings.xml snippet is an example of a configuration to enable manual call obfuscation when a user enters **

<audio>
    <obfuscation>
        <dtmfStart>**</dtmfStart>
        <dtmfStop>##</dtmfStop>
        <dtmfTimeout>2000</dtmfTimeout>
        <stopTimeout>50000</stopTimeout> 
        <toneFile>
            <default>{app}/tones/alaw.wav</default>
            <codec id="0">{app}/tones/ulaw.wav</codec>
            <codec id="8">{app}/tones/alaw.wav</codec>
        </toneFile>
    </obfuscation>
</audio>

The dtmfTimeout element was provided to prevent a situation where extra digits have been erroneously entered, and therefore making it impossible to enter the correct sequence. After the specified DTMF timeout has passed, all the digits previously entered will be cleared. This also ensures that obfuscation does not occur during normal negotiation of DTMF telephone selection menus (inbound or outbound). To set a DTMF entry timeout, specify the value (in milliseconds) using the dtmfTimeout element.

Additionally, an obfuscation timeout can be specified to automatically stop the obfuscation after a specified period of time, to prevent the entire remaining call from being obfuscated in case the user forgets to manually stop the obfuscation. This timeout period can be specified (in milliseconds) using the stopTimeout element.

Custom tones

Custom tones can be added to the call recorder in order to obfuscate part of a call recording. Since the tones are raw byte data that replace portions of the original audio stream, they must respect the codec of the original file, e.g. a-law, u-law, etc., and use the same sample size and rate, e.g. 16-bit, 8 KHz.

Since phone calls can use various codecs (dictated by both parties of a conversation) you should make your customised audio tone available in each format, using the same codecs that your phone system might use.

Once the files have been encoded accordingly, they should be copied to the following location: {app}\ProgramData\Tri-Line\Echo\tones.

To enable the system to use these custom tones during the obfuscation, open the settings.xml file, located in {app}\PrgramData\Tri-Line\Echo and add the following snippet, specifying the filename of the custom tone using the codec element. The id attribute determines the codec type, e.g. "0" = u-law, "8" = a-law, as per RFC3551 (page 32).

<audio>
    <obfuscation>
        <toneFile>
            <default>{app}/tones/alaw.wav</default>
            <codec id="0">{app}/tones/ulaw.wav</codec>
            <codec id="8">{app}/tones/alaw.wav</codec>
        </toneFile>
    </obfuscation>
</audio>