Tone detection system and method
US4521647A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 17, 1984 |
| Grant date | Jun 4, 1985 |
| Priority date | — |
| Expiry date | Feb 17, 2004 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04Q1/46
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
Tone detection apparatus and a corresponding method is disclosed. The improved tone detector and method is for use in a preferred embodiment in a voice message answering system to provide for improved dual tone multi-frequency tone detection where an outgoing analog voice signal is connected to a telephone line. When an incoming call is detected, the tone detector looks at the incoming analog signal and if a dual tone control signal is detected, a filter is switched to filter the outgoing analog signal so that the DTMF tone signal now being detected is filtered out of the outgoing signal. If the incoming signal still detects a tone, the improved tone detector cuts off or disconnects the outgoing signal completely for approximately 20 milliseconds. If a dual tone control signal is still detected, it is determined that it is an incoming control signal and consequently access is required into the voice message system.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.