Method and apparatus for bandwidth reduction
US4255620A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 9, 1978 |
| Grant date | Mar 10, 1981 |
| Priority date | — |
| Expiry date | Jan 9, 1998 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B1/66
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
The bandwidth of human speech signals, 125 to 3000 Hz, is reduced to approximately 125 to 1500 Hz by folding or shifting the high-frequency consonant-band portion, 1000 to 3000 Hz, into the low-frequency vowel-band portion, 125 to 1000 Hz. After transmission, the reduced speech signal is expanded to reconstruct an approximation of the original speech signal. One embodiment features folding (modulator carrier frequency is 3000 Hz) and modulator feedthrough. Another embodiment features shifting (carrier is 1800 Hz) and no modulator feedthrough. Both embodiments boost lower vowel frequencies prior to modulation, and use no switching circuitry.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.