Noise feedback coding system and method for providing generalized noise shaping within a simple filter structure
View Patent ↗A noise feedback coding (NFC) system and method that utilizes a simple and relatively inexpensive general structural configuration, but achieves improved flexibility with respect to controlling the shape of coding noise. The NFC system and method utilizes an all-zero noise feedback filter that is configured to approximate the response of a pole-zero noise feedback filter.
1. An encoder in a noise feedback coding system, comprising:
a first combiner that combines an input audio signal and a predicted audio signal to generate a prediction residual signal;
a second combiner that combines the prediction residual signal with a noise feedback signal to generate a quantizer input signal;
a quantizer that quantizes the quantizer input signal to generate a quantizer output signal;
a third combiner that combines the quantizer input signal and the quantizer output signal to generate a quantization error signal; and
a noise feedback filter that filters the quantization error signal to generate the noise feedback signal, wherein the noise feedback filter is an all-zero filter configured to have a response substantially equal to that of a truncated finite impulse response of a pole-zero filter.
2. The encoder of claim 1 , wherein the input audio signal comprises an input speech signal and wherein the predicted audio signal comprises a predicted speech signal.
3. The encoder of claim 1 , wherein the noise feedback filter is a twelfth order filter.
4. The encoder of claim 1 , wherein the quantizer is a vector quantizer.
5. The encoder of claim 1 , further comprising:
a predictor that receives the input audio signal and generates the predicted audio signal therefrom.
6. The encoder of claim 5 , wherein the predictor comprises a short-term predictor.
7. The encoder of claim 5 , wherein {circumflex over (P)}(z) is a transfer function of the predictor based on quantized predictor coefficients, P(z) is a transfer function of the predictor based on non-quantized predictor coefficients, and the response of the noise feedback filter is defined as a finite impulse response truncation of F(z), wherein
F
(
z
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=
1
-
A
^
(
z
)
A
(
z
/
δ
1
)
A
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z
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δ
2
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,
Â(z)=1−{circumflex over (P)}(z), A(z)=1−P(z), and δ 1 and δ 2 are filter control parameters.
8. A method for encoding a signal in a noise feedback coding system, comprising:
combining an input audio signal and a predicted audio signal to generate a prediction residual signal;
combining the prediction residual signal with a noise feedback signal to generate a quantizer input signal;
quantizing the quantizer input signal to generate a quantizer output signal;
combining the quantizer input signal and the quantizer output signal to generate a quantization error signal; and
filtering the quantization error signal to generate the noise feedback signal, wherein the filtering is performed using an all-zero filter configured to have a response that is defined as a truncated finite impulse response of a pole-zero filter.
9. The method of claim 8 , wherein combining an input audio signal and a predicted audio signal comprises combining an input speech signal and a predicted speech signal.
10. The method of claim 8 , wherein the filtering is performed using a twelfth order all-zero filter.
11. The method of claim 8 , wherein quantizing the quantizer input signal comprises performing vector quantization of the quantizer input signal.
12. The method of claim 8 , further comprising:
predicting the input audio signal to generate the predicted audio signal.
13. The method of claim 12 , wherein predicting the input audio signal comprises performing short-term prediction of the input audio signal.
14. The method of claim 12 , wherein:
predicting the input audio signal comprises predicting the input audio signal using a predictor, wherein {circumflex over (P)}(z) is a transfer function of the predictor based on quantized predictor coefficients and P(z) is a transfer function of the predictor based on non-quantized predictor coefficients; and
filtering the quantization error signal comprises filtering the quantization error signal using an all-zero filter having a response that is defined as a finite impulse response truncation of F(z), wherein
F
(
z
)
=
1
-
A
^
(
z
)
A
(
z
/
δ
1
)
A
(
z
/
δ
2
)
,
Â(z)=1−{circumflex over (P)}(z), A(z)=1−P(z), and δ 1 and δ 2 are filter control parameters.
15. A computer program product comprising a computer useable medium having computer program logic recorded thereon for enabling a processor to encode a signal in a noise feedback coding system, comprising:
means for enabling the processor to combine an input audio signal and a predicted audio signal to generate a prediction residual signal;
means for enabling the processor to combine the prediction residual signal with a noise feedback signal to generate a quantizer input signal;
means for enabling the processor to quantize the quantizer input signal to generate a quantizer output signal;
means for enabling the processor to combine the quantizer input signal and the quantizer output signal to generate a quantization error signal; and
means for enabling the processor to filter the quantization error signal to generate the noise feedback signal, wherein filtering the quantization error signal includes applying an all-zero filter that is configured to have a response that is defined as a truncated finite impulse response of a pole-zero filter.
16. The computer program product of claim 15 , wherein the means for enabling the processor to combine an input audio signal and a predicted audio signal comprises means for enabling the processor to combine an input speech signal and a predicted speech signal.
17. The computer program product of claim 15 , wherein filtering the quantization error signal comprises applying a twelfth order all-zero filter.
18. The computer program product of claim 15 , wherein the means for enabling the processor to quantize the quantizer input signal comprises means for enabling the processor to perform vector quantization of the quantizer input signal.
19. The computer program product of claim 15 , further comprising:
means for enabling the processor to predict the input audio signal to generate the predicted audio signal.
20. The computer program product of claim 19 , wherein the means for enabling the processor to predict the input audio signal comprises means for enabling the processor to perform short-term prediction of the input audio signal.
21. The computer program product of claim 19 , wherein:
the means for enabling the processor to predict the input audio signal comprises means for enabling the processor to predict the input audio signal using a predictor, wherein {circumflex over (P)}(z) is a transfer function of the predictor based on quantized predictor coefficients and P(z) is a transfer function of the predictor based on non-quantized predictor coefficients; and
the means for enabling the processor to filter the quantization error signal comprises means for enabling the processor to filter the quantization error signal using an all-zero filter having a response that is defined as a finite impulse response truncation of F(z), wherein
F
(
z
)
=
1
-
A
^
(
z
)
A
(
z
/
δ
1
)
A
(
z
/
δ
2
)
,
Â(z)=1−{circumflex over (P)}(z), A(z)=1−P(z), and δ 1 and δ 2 are filter control parameters.