Method and system for speech frame error concealment in speech decoding

• US 6,968,309 B1
• Filed: 10/31/2000
• Issued: 11/22/2005
• Est. Priority Date: 10/31/2000
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Vainio, Janne, Mäkinen, Jari, Mikkola, Hannu, Rotola-Pukkila, Jani
• Primary Examiner(s): Knepper, David D.
• Assistant Examiner(s): HAN, QI
• Application Number:
  US09/702,540
• Time in Patent Office: 1,848 Days
• Field of Search: 704/219, 704/223, 704/258, 704/206, 704/207
• US Class Current: 704/219
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 25/93 Discriminating between voiced and unvoiced parts of speech signals G10L25/90 takes precedence

Abstract

A method and system for concealing errors in one or more bad frames in a speech sequence as part of an encoded bit stream received in a decoder. When the speech sequence is voiced, the LTP-parameters in the bad frames are replaced by the corresponding parameters in the last frame. When the speech sequence is unvoiced, the LTP-parameters in the bad frames are replaced by values calculated based on the LTP history along with an adaptively-limited random term.

Claims

1. A method for concealing errors in an encoded bit stream indicative of speech signals received in a speech decoder, wherein the encoded bit stream includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, said method comprising the steps of:

providing an upper limit and a lower limit based on the second long-term prediction lag values;

determining whether the first long-term prediction lag value is within or outside the upper and lower limits;

replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value, when the first long-term prediction lag value is outside the upper and lower limits; and

retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

2. The method of claim 1, further comprising the step of replacing the first long-term prediction gain value in the partially corrupted frame with a third gain value, when the first long-term lag value is outside the upper and lower limits.

3. The method of claim 1, wherein the third lag value is calculated based the second long-term prediction lag values and an adaptively-limited random lag jitter bound by further limits determined based on the second long-term prediction lag values.

4. The method of claim 2, wherein the third gain value is calculated based on of the second long-term prediction gain values and an adaptively-limited random gain jitter bound by limits determined based on the second long-term prediction gain values.

5. A speech signal transmitter and receiver system for encoding speech signals in an encoded bit stream and decoding the encoded bit stream into synthesized speech, wherein the encoded bit stream includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, and a first signal is used to indicate the partially corrupted frame, said system comprising:

a first means, responsive to the first signal, for determining whether the first long term prediction lag is within an upper limit and a lower limit, and for providing a second signal indicative of said determining;

a second means, responsive to the second signal, for replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value when the first long-term prediction lag value is outside the upper and lower limits; and

retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

6. The system of claim 5, wherein the third lag value is determined based on the second long-term prediction lag values and an adaptively-limited random lag jitter.

7. The system of claim 5, wherein the second means further replaces the first long-term prediction gain value in the partially corrupted frame with a third gain value when when the first long-term prediction lag value is outside the upper and lower limits.

8. The system of claim 7, wherein the third gain value is determined based on the second long-term prediction gain values and an adaptively-limited random gain jitter.

9. A decoder for synthesizing speech from an encoded bit stream, wherein the encoded bit stream includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, and a first signal is used to indicate the partially corrupted frame, said decoder comprising:

a first means, responsive to the first signal, for determining whether the first long-term prediction lag is within an upper limit and a lower limit, and for providing a second signal indicative of said determining;

a second means, responsive to the second signal, for replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value when the first long-term prediction lag value is outside the upper and lower limits; and

retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

10. The decoder of claim 9, wherein the third lag value is determined based on the second long-term prediction lag values and an adaptively-limited random lag jitter.

11. The decoder of claim 9, wherein the second means further replaces the first long-term gain value in the partially corrupted frame with a third gain value when the first long-term prediction lag value is outside the upper and lower limits.

12. The decoder of claim 11, wherein the third gain value is determined based on the second long-term prediction gain values and an adaptively-limited random gain jitter.

13. A mobile station, which is arranged to receive an encoded bit stream containing speech data indicative of speech signals, wherein the encoded bit stream includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, and wherein a first signal is used to indicate the corrupted frame, said mobile station comprising:

a first means, responsive to the first signal, for determining whether the first long-term prediction lag is within an upper limit and a lower limit, and for providing a second signal indicative of said determining;

a second means, responsive to the second signal, for replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value when the first long-term prediction lag value is outside the upper and lower limits; and

retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

14. The mobile station of claim 13, wherein the third lag value is determined based on the second long-term prediction lag values and an adaptively-limited random lag jitter.

15. The mobile station of claim 13, wherein the second means further replaces the first long-term gain value in the partially corrupted frame with a third gain value when the first long-term prediction lag value is outside the upper and lower limits.

16. The mobile station of claim 15, wherein the third gain value is determined based on the second long-term prediction gain values and an adaptively-limited random gain jitter.

17. An element in a telecommunication network, which is arranged to receive an encoded bit stream containing speech data from a mobile station, wherein the speech data includes a plurality of speech frames arranged in speech sequences, and the speech frames include at least one partially corrupted frame preceded by one or more non-corrupted frames, wherein the partially corrupted frame includes a first long-term prediction lag value and a first long-term prediction gain value, and the non-corrupted frames include second long-term prediction lag values and second long-term prediction gain values, and wherein a first signal is used to indicate the corrupted frame, said element comprising:

a first means, responsive to the first signal, for determining whether the first long-term prediction lag is within an upper limit and a lower limit, and for providing a second signal indicative of said determining;

a second means, responsive to the second signal, for replacing the first long-term prediction lag value in the partially corrupted frame with a third lag value when the first long-term prediction lag value is outside the upper and lower limits; and

retaining the first long-term prediction lag value in the partially corrupted frame when the first long-term prediction lag value is within the upper and lower limits.

18. The element of claim 17, wherein the third long-term prediction lag value is determined based on the second long-term prediction lag values and an adaptively-limited random lag jitter.

19. The element of claim 17, wherein the third means further replaces the first long-term prediction gain value with a third gain value when the first long-term lag value is outside the upper and lower limits.

20. The element of claim 19, wherein the third gain value is determined based on the second long-term prediction gain values and an adaptively-limited random gain jitter.