[54] EMBEDDED SIGNALLING
[75] Inventors: Robert D. Preuss, Boston, Mass.;
Salim E. Roukos, Scarsdale, N.Y.; A.
W. F. Huggins, Arlington, Mass.;
Herbert Gish, Newton, Mass.;
Marcos A. Bergamo, Wellesley,
Mass.; Patrick M. Peterson,
Cambridge, Mass.; Alan G. Derr,
Westford, Mass.
[73] Assignee: Bolt Beranek and Newman Inc.,
Cambridge, Mass.
[21] Appl. No.: 808,913
[22] Filed: Dec. 17,1991
[51] Int. CI.5 G10L 3/00
[52] U.S. CI 395/2.14
[58] Field of Search 375/1, 122; 358/143;
370/110.1; 395/2, 2.1, 2.14; 381/29-40
[56] References Cited
U.S. PATENT DOCUMENTS
3,004,104 10/1961 Hembrooke 370/37
4,395,600 7/1983 Lundy et al 381/73.1
4,425,661 1/1984 Moses et al 375/1
4,593,389 6/1986 Wurzburg et al 370/110.1
4,775,901 10/1988 Nakano 360/60
4,777,529 10/1988 Schultz et al 358/143
4,903,301 2/1990 Kondo et al 381/30
4,943,973 7/1990 Werner 375/1
4,965,680 10/1990 Endoh 360/60
4,972,471 11/1990 Gross et al 380/3
4,979,210 12/1990 Nagata et al 380/3
5,212,551 5/1993 Conanan 358/143
Primary Examiner—David D. Knepper
Attorney, Agent, or Firm—Henry D. Pahl, Jr.
[57] ABSTRACT
A code signal representing a sequence of code symbols carrying digital information is generated with the frequency components of the code signal being essentially confined to a preselected signalling band lying within the bandwidth of an audio signal within which the code signal is to be embedded. The audio signal is continuously frequency analyzed over a frequency band encompassing the signalling band and the code signal is dynamically filtered as a function of the analysis thereby to provide a modified code signal with frequency components which are, at each time instant, essentially a preselected small proportion of the levels of the corresponding audio signal frequency components. Accordingly, the modified code signal can be combined with the audio signal to obtain a composite audio signal which is not readily distinguishable from the original audio signal by listening. Furthermore, the digital information can be recovered from the composite audio signal by a procedure which is essentially the compliment of that used to obtain the composite audio signal.
25 Claims, 11 Drawing Sheets
