Adaptive approach to improve G.711 perceptual quality
In order to achieve the best improvement of ITU G.711 related codec perceptual quality, perceptual weighting controlling parameter(s) should be at least adaptive to relative quantization error statistics or adaptive to signal level. When the relative quantization error statistics are larger or the signal level is lower, the perceptual weighting should be “stronger”, which means α in (5) is smaller; when the relative quantization error statistics are smaller or the signal level is larger, the perceptual weighting should be “weaker”, which means α in (5) is larger.
1. A method of improving a perceptual weighting filter W(z) or a perceptual noise shaping filter F(z)=W(z)−1, used to enhance perceptual performance of a G.711 codec, the method comprising:
i. inputting an unquantized signal sample to a G.711 encoder;
ii. encoding said unquantized signal via the G.711 encoder to produce a coded bitstream using W(z) or F(z) as follows:
W
(
z
)
=
A
(
z
/
α
)
=
1
+
∑
i
=
1
P
a
i
·
α
i
·
z
-
i
,
i
=
1
,
2
,
…
,
P
F
(
z
)
=
W
(
z
)
-
1
=
∑
i
=
1
P
a
i
·
α
i
·
z
-
i
,
i
=
1
,
2
,
…
,
P
A
(
z
)
=
1
+
∑
i
=
1
P
a
i
·
z
-
i
,
i
=
1
,
2
,
…
,
P
where A(z) is an LP (Linear Prediction) predictor obtained from analyzing an input signal, {a i , i=1, 2, . . . , P} are the LP predictor coefficients, P is the LP predictor order and α is a controlling parameter controlling W(z) or F(z),
wherein the controlling parameter α depends on an input signal level;
when the input signal level becomes low (towards zero), α is towards 0;
iii. receiving said bitstream at a decoder; and
iv. outputting an enhanced decoded signal.
2. The method of claim 1 , wherein the G.711 codec performs as a core layer of a scalable coder.
3. The method of claim 1 , wherein the G.711 codec is compatible with ITU (International Telecommunication Union) G.711 A-law or μ-law codec standard.
4. A method of improving a perceptual weighting filter W(z) or a perceptual noise shaping filter F(z)=W(z)−1, used to enhance perceptual performance of a G.711 codec, the method comprising:
i. inputting an unquantized signal sample to a G.711 encoder;
ii. encoding said unquantized signal via the G.711 encoder to produce a coded bitstream using W(z) or F(z) as follows:
W(z) or F(z) is controlled by one or several parameters;
at least one of the parameters controlling W(z) or F(z) depends on an input signal level;
when the input signal level becomes low (towards zero), W(z) is towards 1 or equivalently F(z) is towards 0;
iii. receiving said bitstream at a decoder; and
iv. outputting an enhanced decoded signal.
5. The method of claim 4 , wherein the perceptual weighting filter W(z) or the perceptual noise shaping filter F(z) is defined by the following equations:
W
(
z
)
=
A
(
z
/
α
)
=
1
+
∑
i
=
1
P
a
i
·
α
i
·
z
-
i
,
i
=
1
,
2
,
…
,
P
F
(
z
)
=
W
(
z
)
-
1
=
∑
i
=
1
P
a
i
·
α
i
·
z
-
i
,
i
=
1
,
2
,
…
,
P
A
(
z
)
=
1
+
∑
i
=
1
P
a
i
·
z
-
i
,
i
=
1
,
2
,
…
,
P
where A(z) is an LP (Linear Prediction) predictor obtained from analyzing an input signal, {a i , i=1, 2, . . . , P} are the LP predictor coefficients, P is the LP predictor order and α is the controlling parameter controlling W(z) or F(z).
6. The method of claim 4 , wherein the perceptual weighting filter W(z) or the perceptual noise shaping filter F(z) is defined by the following equations:
W
(
z
)
=
A
(
z
/
α
)
A
(
z
/
β
)
F
(
z
)
=
W
(
z
)
-
1
A
(
z
)
=
1
+
∑
i
=
1
P
a
i
·
z
-
i
,
i
=
1
,
2
,
…
,
P
where A(z) is an LP (Linear Prediction) predictor obtained from analyzing an input signal; {a i , i=1, 2, . . . , P} are the LP predictor coefficients; P is the LP predictor order; α and β(β<α) are the controlling parameters controlling W(z) or F(z).
7. The method of claim 4 , wherein the perceptual weighting filter W(z) or the perceptual noise shaping filter F(z) is defined by the following equations:
W
(
z
)
=
A
(
z
/
α
)
1
+
β
·
z
-
1
F
(
z
)
=
W
(
z
)
-
1
A
(
z
)
=
1
+
∑
i
=
1
P
a
i
·
z
-
i
,
i
=
1
,
2
,
…
,
P
where A(z) is an LP (Linear Prediction) predictor obtained from analyzing an input signal; {a i , i=1, 2, . . . , P} are the LP predictor coefficients; P is the LP predictor order; α and β (β<α) are the controlling parameters controlling W(z) or F(z).
8. The method of claim 4 , wherein the G.711 codec performs as a core layer of a scalable coder.
9. The method of claim 4 , wherein the G.711 codec is compatible with ITU (International Telecommunication Union) G.711A-law or μ-law codec standard.