Some recorded files with human voice or music can repeatedly cause voice processing hardware to erroneously recognize DTMF sounds on the telephone line. This is called talk-off. What happens, in fact, is that the voice of the speaker, or the music being played, contains pairs of frequencies very similar to the DTMF frequencies generated by telephone keypads. This typically happens only once in a while, and only on a small number of files.
Vox Studio can fix this for you by removing the DTMF frequencies from your sound file. One pass through Vox Studio's DTMF attenuator usually fixes this. Of course, removing sound at various places in the frequency spectrum does affect sound quality somewhat. So, use this only when you need it, and only on the files that need it. We would advise you to experiment with this function before you start using it on a live system. Vox Studio's DTMF detection capability allows automatic flagging of files that may contain such erroneous DTMF tones. There is absolutely no justification to filter all your files for DTMF.
Vox Studio provides for selection of weak, medium or strong DTMF filtering.