Apparatus and method for audible signaling tone recognition
US5311589A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 31, 1992 |
| Grant date | May 10, 1994 |
| Priority date | — |
| Expiry date | Mar 31, 2012 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M3/428
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A method and apparatus for detecting dual-tone, multi-frequency (DTMF) digits and call progress tones by determining the amplitudes of preselected frequencies in a signal over a predetermined time period, and determining a candidate tone by selecting two of the preselected frequencies with the highest amplitudes and comparing the two selected frequencies to known DTMF and call progress tone frequencies. The amplitudes of the two selected frequencies are then tested against predefined thresholds corresponding to a candidate tone having the two selected frequencies. The candidate tone in the current time period is tested against candidate tones in previous time periods for consistency. If the candidate tone is a DTMF digit and passed all of the tests, then the DTMF digit is returned. If the candidate tone is a call progress tone, the pattern of the candidate tone over a plurality of predetermined time periods is recorded and tested against known patterns of the candidate tone. If the candidate tone meets all of the above tests, the call progress tone is returned.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.