Efficient excitation quantization in noise feedback coding with general noise shaping

1. In a Noise Feedback Coding (NFC) system operable in a ZERO-STATE condition and a ZERO-INPUT condition, the NFC system including a long-term noise feedback filter having a first filter memory and a short-term noise feedback filter having a second filter memory, a method of updating the first and second filter memories, comprising:

(a) producing a first ZERO-STATE contribution to the first filter memory and a second ZERO-STATE contribution to the second filter memory when the NFC system is in the ZERO-STATE condition;

(b) producing a first ZERO-INPUT contribution to the first filter memory and a second ZERO-INPUT contribution to the second filter memory when the NFC system is in the ZERO-INPUT condition;

(c) updating the first filter memory as a function of both the first ZERO-STATE contribution and the first ZERO-INPUT contribution; and

(d) updating the second filter memory as a function of both the second ZERO-STATE contribution and the second ZERO-INPUT contribution.

2. The method of claim 1 , wherein step (c) comprises

adding together the first ZERO-STATE and the first ZERO-INPUT contributions to produce a first filter memory update; and

updating the first filter memory with the first filter memory update.

3. The method of claim 1 , further comprising:

prior to step (a), searching N VQ codevectors associated with the NFC system for a best VQ codevector,

wherein step (a) comprises producing the first ZERO-STATE contribution and the second ZERO-STATE contribution corresponding to the best VQ codevector.

4. The method of claim 1 , wherein the short-term noise feedback filter includes

an all-zero filter section, and

an all-pole filter section.

5. The method of claim 4 , wherein the all-zero filter section is of the form

F

sz

⁢

(

z

)

=

∑

i

=

1

N

N1

-

1

⁢

a

1

·

(

γ

p

i

-

γ

z

i

)

·

z

-

1

where N NFF is the order of the all-zero filter section,

a i , is i th prediction coefficient,

γ z is a bandwidth expansion factor for the all-zero filter section, and

γ p is a bandwidth expansion factor for the all-pole filter section.

6. The method of claim 4 , wherein the all-pole filter section is of the form:

1

F

sp

⁢

(

z

)

=

1

1

-

∑

i

=

1

N

N1

-

1

⁢

a

i

·

γ

p

i

·

z

-

1

.

7. A computer readable medium carrying one or more sequences of one or more instructions for execution by one or more processors to perform, in a Noise Feedback Coding (NFC) system operable in a ZERO-STATE condition and a ZERO-INPUT condition, the NFC system including a long-term noise feedback filter having a first filter memory and a short-term noise feedback filter having a second filter memory, a method of updating the first and second filter memories, the instructions when executed by the one or more processors, causing the one or more processors to perform the steps of:

(a) producing a first ZERO-STATE contribution to the first filter memory and a second ZERO-STATE contribution to the second filter memory when the NFC system is in the ZERO-STATE condition;

(b) producing a first ZERO-INPUT contribution to the first filter memory and a second ZERO-INPUT contribution to the second filter memory when the NFC system is in the ZERO-INPUT condition;

(c) updating the first filter memory as a function of both the first ZERO-STATE contribution and the first ZERO-INPUT contribution; and

(d) updating the second filter memory as a function of both the second ZERO-STATE contribution and the second ZERO-INPUT contribution.

8. The computer readable medium of claim 7 , wherein step (c) comprises:

adding together the first ZERO-STATE and the first ZERO-INPUT contributions to produce a first filter memory update; and

updating the first filter memory with the first filter memory update.

9. The computer readable medium of claim 7 , carrying the one or more instructions, causing the one or more processors to perform, prior to step (a), the further step of:

searching N VQ codevectors associated with the NFC system for a best VQ codevector,

wherein step (a) comprises producing the first ZERO-STATE contribution and the second ZERO-STATE contribution corresponding to the best VQ codevector.

10. The computer readable medium of claim 7 , wherein the short-term noise feedback filter includes

an all-zero filter section, and

an all-pole filter section.

11. A Noise Feedback Coding (NFC) system operable in a ZERO-STATE condition and a ZERO-INPUT condition, the NFC system including a long-term noise feedback filter having a first filter memory and a short-term noise feedback filter having a second filter memory, the system comprising:

first means for producing a first ZERO-STATE contribution to the first filter memory and a second ZERO-STATE contribution to the second filter memory when the NFC system is in the ZERO-STATE condition;

second means for producing a first ZERO-INPUT contribution to the first filter memory and a second ZERO-STATE contribution to the second filter memory when the NFC system is in the ZERO-INPUT condition;

third means for updating the first filter memory as a function of both the first ZERO-STATE contribution and the first ZERO-INPUT contribution; and

fourth means for updating the second filter memory as a function of both the second ZERO-STATE contribution and the second ZERO-INPUT contribution.

12. The system of claim 11 , wherein the third means includes:

means for adding together the first ZERO-STATE and the first ZERO-INPUT contributions to produce a first filter memory update; and

means for updating the first filter memory with the first filter memory update.

13. The system of claim 11 , further comprising:

fourth means for searching N VQ codevectors associated with the NFC system for a best VQ codevector,

wherein the first means includes means for producing the first ZERO-STATE contribution and the second ZERO-STATE contribution corresponding to the best VQ codevector.

14. The system of claim 11 , wherein the short-term noise feedback filter includes

an all-zero filter section, and

an all-pole filter section.