1. A. Hoagland, AIEE Trans. Communications 75, 605 (1956).
2. J. J. Miyata and R. R. Hartel, IRE Trans. Electr. Comp. EC-8, 159 (1959).
3. D. F. Eldridge, IRE Trans. Audio AU-8, 42 (1960).
4. K. Teer, Philips Res. Repts 16, 469 (1961).
5. G. C. Feth, AIEE Trans. Communications 81, 267 (1962)