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| US3946162 | 17 May 1974 | 23 Mar 1976 | International Standard Electric Corporation | System for transferring wideband sound signals |
| US3952164 | 18 Jul 1974 | 20 Apr 1976 | Telecommunications Radioelectriques et Telephoniques T.R.T.
Etat Francais | Vocoder system using delta modulation |
| US3988546 | 13 Sep 1974 | 26 Oct 1976 | General Signal Corporation | System for audibly recognizing an aurally unclassifiable signal |
| US4181822 | 7 Mar 1978 | 1 Jan 1980 | Bell & Howell Company | Bandsplitter systems |
| US4229622 | 14 Mar 1978 | 21 Oct 1980 | The Post Office | Multiplexing speech signals |
