Speech enhancement system having dynamic gain control

• US 4,747,143 A
• Filed: 07/12/1985
• Issued: 05/24/1988
• Est. Priority Date: 07/12/1985
• Status: Expired due to Fees

• Current Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Kroeger, Brian W., Kurtz, John J.
• Primary Examiner(s): Kemeny, E. S.
• Application Number:
  US06/755,235
• Time in Patent Office: 1,047 Days
• Field of Search: 381/46, 381/47, 381/104-108, 381/94, 455/218-222, 455/246, 455/247, 455/245, 455/234, 379/421, 330/134, 330/279, 330/132, 330/136
• US Class Current: 704/225
• CPC Class Codes: G10L 21/0208 Noise filtering

Abstract

An arrangement for a speech enhancement processor which maintains the processed speech at a constant level regardless of large changes in the associated noise level. The composite speech and noise signal is applied to a first AGC circuit and then to a speech enhancement system which removes tonal, impulse, and wideband noises from the signal. The extracted noise power estimates are subtracted from the constant amplitude signal to provide a gain control signal value to which the gain of a second variable gain amplifier is inversely proportional. The amplifier multiplies the processed speech output from the enhancement system and, because of the variable gain control, provides an output speech signal having short-term amplitude levels which correspond to those of the input speech signal, and having a constant long-term amplitude level.

Claims

1. A speech enhancement system having dynamic gain control, said system comprising:

means for providing a constant amplitude composite speech and noise signal from an applied variable amplitude composite speech and noise signal;

means for processing said constant amplitude composite signal, said processing means performing one or more processes for extracting noise power from said constant amplitude composite signal, thereby providing one or more extracted noise power values and a processed speech output;

means for subtracting all of said noise power values from said constant amplitude composite signal to provide a gain control signal value;

multiplying means for amplifying said processed speech output by a variable ratio; and

means for controlling the variable ratio of said multiplying means, with the controlling being dependent upon said gain control signal value.

2. The speech enhancement system of claim 1 wherein the controlling means varies the ratio of the multiplying means inversely with respect to the gain control signal value.

3. The speech enhancement system of claim 1 wherein the controlling means maintains the ratio of the multiplying means equal to a constant divided by the gain control signal value.

4. The speech enhancement system of claim 1 wherein one of the processes for extracting noise power provides noise power values corresponding to the power of tonal noises extracted from the constant amplitude composite signal.

5. The speech enhancement system of claim 1 wherein one of the processes for extracting noise power provides noise power values corresponding to the power of impulse noises extracted from the constant amplitude composite signal.

6. The speech enhancement system of claim 1 wherein one of the processes for extracting noise power provides noise power values corresponding to the power of wideband noises extracted from the constant amplitude composite signal.

7. A speech enhancement system having dynamic gain control, said system comprising:

an automatic gain control means for providing a constant amplitude composite speech and noise signal from an applied variable amplitude composite speech and noise signal;

means for digitally processing said constant amplitude composite signal, said processing means being capable of extracting tonal, impulse, and wideband noise powers from said constant amplitude composite signal, thereby providing three instantaneous extracted noise power values and a processed speech output;

means for subtracting all three of said noise power values from said constant amplitude composite signal to provide a gain control signal value;

multiplying means for amplifying said processed speech output by a variable ratio; and

means for maintaining the amplifying ratio of said multiplying means equal to a constant divided by said gain control signal value.

8. A method of speech enhancement having dynamic gain control, said method comprising the steps of:

maintaining constant the level of a composite speech and voice signal;

extracting noise power from said constant level composite signal to provide at least one instantaneous noise power signal value and a processed speech output;

subtracting said noise power signal values from the constant level composite signal to provide a gain control signal;

multiplying said processed speech output by a variable amount; and

controlling the variable multiplying amount with the gain control signal.

9. The method of speech enhancement of claim 8 wherein the variable multiplying amount is controlled sufficiently to maintain the amount equal to a constant divided by the gain control signal.

10. The method of speech enhancement of claim 8 wherein said one noise power signal value corresponds to extracted tonal noises.

11. The method of speech enhancement of claim 8 wherein the one noise power signal value corresponds to extracted impulse noises.

12. The method of speech enhancement of claim 8 wherein the one noise power signal value corresponds to extracted wideband noises.