Accession Number:

ADA277652

Title:

Noise Cancellation for CELP Voice Encoders in an F/A-18 Noise Environment

Descriptive Note:

Interim rept. Jan 1991-Jan 1993

Corporate Author:

NAVAL RESEARCH LAB WASHINGTON DC

Personal Author(s):

Report Date:

1994-03-18

Pagination or Media Count:

23.0

Abstract:

Because of the severe noise environment in the Navys FA-18 jet aircraft, it has always been very difficult to achieve highly intelligible speech using low data rate voice encoders such as the 2.4 kbps LPC-10. As a result, all voice encoding has been done with a high data rate 16.0 kbps CVSD algorithm. The main focus of this research was to develop a technique that could retain the acceptable intelligibility of the high rate encoders while still significantly lowering the data rate required. To achieve these results, a noise cancellation preprocessor was developed to be used in tandem with the new 4.8 . kbps CELP encoder that is being implemented in the STU-III. While many noise reduction techniques were investigated, the best results were accomplished by first reducing the noise through spectral subtraction and then enhancing the important resonant formants of the speech. The results indicated that when the noise cancellation preprocessor was added to the CELP encoder, the DRT intelligibility scores were improved by a significant 5.0 points, making the speech much more acceptable for possible use in the FA-18. Noise cancellation, Spectral subtraction. Digital filtering.

Subject Categories:

  • Attack and Fighter Aircraft
  • Cybernetics
  • Acoustics
  • Voice Communications

Distribution Statement:

APPROVED FOR PUBLIC RELEASE