Subband decoding method and apparatus

• US 5,054,075 A
• Filed: 09/05/1989
• Issued: 10/01/1991
• Est. Priority Date: 09/05/1989
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Kotzin, Michael D., Hong, Daehyoung
• Primary Examiner(s): Kemeny, Emanuel S.
• Assistant Examiner(s): Doerrler, Michelle
• Application Number:
  US07/403,245
• Time in Patent Office: 756 Days
• Field of Search: 381/31-41, 381/29, 381/30, 381/46, 381/47, 381/51
• US Class Current: 704/226
• CPC Class Codes: G10L 19/028 Noise substitution, i.e. substituting non-tonal spectral components by noisy source comfort noise for discontinuous speech transmission G10L19/012
• CPC Class Codes: H04B 1/667 using a division in frequency subbands for TV signals H04N19/63

Abstract

An subband coding system encoder is provided for improving the quality of a reconstructed speech signal. Briefly, the improved subband coding system encoder includes means for improving the selection of the waveform/noise fill gain factor. The improved selection method, according to the invention, is based on the quasi-stationary characteristic of speech, that is, that the short-time frequency spectrum of a speech signal varies slowly with time. Moreover, the amount of fill energy is adaptively determined for each subband according to the shape of the frequency spectrum for each speech frame.

Claims

1. In a subband coding system including an encoder having an input signal and a decoder, a method for providing an improved reconstructed signal at the decoder, comprising the following steps:

(a) providing a partially reconstructed signal based on information received from the encoder;

(b) receiving from the encoder N subband energy values E_k, where k varies from 1-N, each E_k based on the energy present in a particular spectral subband of the original input signal;

(c) providing N noise/waveform fill signals, each having an energy value E'"'"'_k, where the E'"'"'_k is provided by the following steps;

(c₁) computing values A, B which minimize ##EQU3## (c₂) computing N values Z_k based on E_k -(Ak+B), where k varies from 1-N;

(c₃) identifying the largest Z_k (Z_k|max);

(c₄) computing N values E'"'"'_k based on E_k -ξ

(Z_k|max -Z_k), where k varies from 1-N and ξ

is a predetermined constant;

(d) combining the noise/waveform fill signals with said partially reconstructed signal.

2. The method of claim 1 wherein ξ

is generally=0.3.

3. The method of claim 1 wherein N=11.

4. A subband coding system including an encoder having an input signal and a decoder, said decoder having means for providing an improved reconstructed signal, comprising:

means for providing a partially reconstructed signal based on information received from the encoder;

means for receiving from the encoder N subband energy values E_k, where k varies from 1-N, each E_k based on the energy present in a particular spectral subband of the original input signal;

means for providing N noise/waveform fill signals, each having an energy value E'"'"'_k, including means for providing the E'"'"'_k, comprising;

means for computing values A, B which minimize ##EQU4## means for computing N values Z_k based on E_k -(Ak+B), where k varies from 1-N;

means for identifying the largest Z_k (Z_k|max);

means for computing N values E'"'"'_k based on E_k -ξ

(Z_k|max -Z_k), where k varies from 1-N and ξ

is a predetermined constant;

means for combining the noise/waveform fill signals with said partially reconstructed signal.

5. The subband coding system of claim 4 wherein ξ

is generally=0.3.

6. The subband coding system of claim 4 wherein N=11.

7. A subband coding system including an encoder having an input signal and a decoder, said decoder being arranged for providing an improved reconstructed signal according to the method comprising the following steps:

(a) providing a partially reconstructed signal based on information received from the encoder;

(b) receiving from the encoder N subband energy values E_k, where k varies from 1-N, each E_k based on the energy present in a particular spectral subband of the original input signal;

(c) providing N noise/waveform fill signals, each having an energy value E'"'"'_k, where the E'"'"'_k is provided by the following steps;

(c₁) computing values A, B which minimize ##EQU5## (c₂) computing N values Z_k based on E_k -(Ak+B), where k varies from 1-N;

(c₃) identifying the largest Z_k (Z_k|max);

(c₄) computing N values E'"'"'_k based on E_k -ξ

(Z_k|max -Z_k), where k varies from 1-N and ξ

is a predetermined constant;

(d) combining the noise/waveform fill signals with said partially reconstructed signal.

8. The subband coding system of claim 7 wherein ξ

is generally=0.3.

9. The subband coding system of claim 7 wherein N=11.

10. A subband coding system including an encoder having an input signal and a decoder, said decoder having a computing means such as a microprocessor or a digital signal processor programmed for providing an improved reconstructed signal according to the method comprising the following steps:

(a) providing a partially reconstructed signal based on information received from the encoder;

(b) receiving from the encoder N subband energy values E_k, where k varies from 1-N, each E_k based on the energy present in a particular spectral subband of the original input signal;

(c) providing N noise/waveform fill signals, each having an energy value E'"'"'_k, where the E'"'"'_k is provided by the following steps;

(c₁) computing values A, B which minimize ##EQU6## (c₂) computing N values Z_k based on E_k -(Ak+B), where k varies from 1-N;

(c₃) identifying the largest Z_k (Z_k|max);

(c₄) computing N values E'"'"'_k based on E_k -ξ

(Z_k|max -Z_k), where k varies from 1-N and ξ

is a predetermined constant;

(d) combining the noise/waveform fill signals with said partially reconstructed signal.

11. The subband coding system of claim 10 wherein ξ

is generally=0.3.

12. The subband coding system of claim 10 wherein N=11.

13. In a subband coding system including an encoder having an input signal and a decoder, a method for operating a computer such as a microprocessor or a digital signal processor for providing an improved reconstructed signal at the decoder, the method comprising the following steps:

(a) providing a partially reconstructed signal based on information received from the encoder;

(b) receiving from the encoder N subband energy values E_k, where k varies from 1-N, each E_k based on the energy present in a particular spectral subband of the original input signal;

(c) providing N noise/waveform fill signals, each having an energy value E'"'"'_k, where the E'"'"'_k is provided by the following steps;

(c₁) computing values A, B which minimize ##EQU7## (c₂) computing N values Z_k based on E_k -(Ak+B), where k varies from 1-N;

(c₃) identifying the largest Z_k (Z_k |_max);

(c₄) computing N values E'"'"'_k based on E_k -ξ

(Z_k |_max -Z_k), where k varies from 1-N and ξ

is a predetermined constant;

(d) combining the noise/waveform fill signals with said partially reconstructed signal.

14. The method of claim 13 wherein ξ

is generally=0.3.

15. The method of claim 13 wherein N=1.