Signal compressors and expanders
US3978409A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 7, 1974 |
| Grant date | Aug 31, 1976 |
| Priority date | — |
| Expiry date | Jun 7, 1994 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N5/911
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
The invention concerns a dynamic range compressor type encoder or expander type decoder, in which a main signal component in a main path is boosted or bucked by a further signal component derived from a point in the main path by a further path having the characteristics of so restricting the further signal component that the boosting or bucking action is only appreciable below a low level threshold. In the present invention the further signal component is a difference signal formed between a direct signal derived from a point in the main path and a delayed version of either the same signal or of another signal derived from another point in the main path. At the frequency equal to the reciprocal of the delay, and at harmonics of this frequency, the direct and delayed signals cancel. The compressor or expander action, and hence noise reduction action, takes place only at intervening frequencies. The invention enables carrier components or other repetitive components of signals to be excluded from the compressor or expander action (which they would otherwise choke).
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.