Dynamic expander
US3978423A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Aug 19, 1974 |
| Grant date | Aug 31, 1976 |
| Priority date | — |
| Expiry date | Aug 19, 1994 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03G7/004
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A dynamic expander which is particularly suitable for restoring the original dynamic range of prerecorded stereo sound program material is disclosed. In this embodiment, the expander comprises first and second variable gain amplifiers respectively coupled to a stereo input. The gain of the amplifiers is controlled by a common slow-attack, slow-decay time-constant circuit. An input of the time-constant circuit is coupled to the stereo input and the time-constant circuit responds thereto to provide a control signal which is indicative of the volume of the program material but which varies in accordance with the characteristics of a non-linear element in the time-constant circuit and with the slow-attack and slow-decay characteristics of the time-constant circuit. The control signal of the time-constant circuit drives a light-emitting-diode (LED) which, in turn, determines the resistance of a pair of matched, light-controlled-resistors (LCR's). Each LCR acts linearly and controls the gain of a respective one of the variable gain amplifiers in accordance with the resistance of that LCR.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.