Method and apparatus for suppressing background noise in a digital telephone system
US3995217A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Mar 21, 1974 |
| Grant date | Nov 30, 1976 |
| Priority date | — |
| Expiry date | Mar 21, 1994 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/253
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
An apparatus for suppressing background noise in a companded delta modulated telephone system. The apparatus includes a comparator for comparing a signal related to the analogue input signal to an encoder of the system with a reference signal. The comparator provides an output to reduce the rate of occurrence of a succession of bits which cause companding within the encoder when the reference signal exceeds the other signal to the comparator. This is achieved by altering the step size of a feedback signal within the encoder or modifying the output from the encoder by removing or inverting one of the compand bits. The reference signal is higher than a signal generated by background noise and consequently for signals below the reference signal the decoder reconstructs an analogue signal which is lower in level than the input signal. A method for achieving the result is also claimed.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.