Method and device for frequency-selective pitch enhancement of synthesized speech
View Patent ↗In a method and device for post-processing a decoded sound signal in view of enhancing a perceived quality of this decoded sound signal, the decoded sound signal is divided into a plurality of frequency sub-band signals, and post-processing is applied to at least one of the frequency sub-band signal. After post-processing of this at least one frequency sub-band signal, the frequency sub-band signals may be added to produce an output post-processed decoded sound signal. In this manner, the post-processing can be localized to a desired sub-band or sub-bands with leaving other sub-bands virtually unaltered.
1. A method for post-processing a decoded sound signal in view of enhancing a perceived quality of said decoded sound signal, comprising:
dividing the decoded sound signal into a plurality of frequency sub-band signals; and
applying post-processing to only a part of the frequency sub-band signals;
wherein applying post-processing to only a part of the frequency sub-band signals comprises pitch enhancing the frequency sub-band signals only in a lower frequency band of the decoded sound signal.
2. A post-processing method as defined in claim 1 , further comprising summing the frequency sub-band signals, after post-processing of said part of the frequency sub-band signals, to produce an output post-processed decoded sound signal.
3. A post-processing method as defined in claim 1 , wherein pitch enhancing comprises adaptively filtering said part of the frequency sub-band signals.
4. A post-processing method as defined in claim 1 , wherein dividing the decoded sound signal into a plurality of frequency sub-band signals comprises sub-band filtering the decoded sound signal to produce the plurality of frequency sub-band signals.
5. A post-processing method as defined in claim 1 , wherein, for said part of the frequency sub-band signals:
pitch enhancing comprises adaptively filtering the decoded sound signal; and
dividing the decoded sound signal comprises sub-band filtering the adaptively filtered decoded sound signal.
6. A post-processing method as defined in claim 1 , wherein:
dividing the decoded sound signal into a plurality of frequency sub-band signals comprises:
a high-pass filtering of the decoded sound signal to produce a frequency high-band signal; and
a first low-pass filtering of the decoded sound signal to produce a frequency low-band signal; and
pitch enhancing comprises:
pitch enhancing the decoded sound signal prior to the first low-pass filtering of the decoded sound signal to produce the frequency low-band signal.
7. A post-processing method as defined in claim 6 , further comprising a second low-pass filtering of the decoded sound signal prior to pitch enhancing said decoded sound signal.
8. A post-processing method as defined in claim 6 , further comprising summing the frequency high-band and low-band signals to produce an output post-processed decoded sound signal.
9. A post-processing method as defined in claim 1 , wherein:
dividing the decoded sound signal into a plurality of frequency sub-band signals comprises:
band-pass filtering the decoded sound signal to produce a frequency upper-band signal; and
low-pass filtering the decoded sound signal to produce a frequency lower-band signal; and
pitch enhancing comprises:
pitch enhancing the decoded sound signal prior to low-pass filtering the decoded sound signal to produce a frequency lower-band signal.
10. A post-processing method as defined in claim 9 , further comprising summing the frequency upper-band and lower-band signals to produce an output post-processed decoded sound signal.
11. A post-processing method as defined in claim 1 , wherein:
dividing the decoded sound signal into a plurality of frequency sub-band signals comprises:
low-pass filtering the decoded sound signal to produce a frequency low-band signal; and
pitch enhancing comprises:
pitch enhancing the frequency low-band signal.
12. A post-processing method as defined in claim 11 , wherein pitch enhancing comprises processing the decoded sound signal through an inter-harmonic filter for inter-harmonic attenuation of the decoded sound signal.
13. A post-processing method as defined in claim 12 , wherein pitch enhancing comprises multiplying the inter-harmonic filtered decoded sound signal by an adaptive pitch enhancement gain.
14. A post-processing method as defined in claim 12 , further comprising low-pass filtering the decoded sound signal prior to processing the decoded sound signal through the inter-harmonic filter.
15. A post-processing method as defined in claim 11 , further comprising summing the decoded sound signal and the frequency low-band signal to produce an output post-processed decoded sound signal.
16. A post-processing method as defined in claim 11 , wherein pitch enhancing comprises processing the decoded sound signal through an inter-harmonic filter having the following transfer function:
y
[
n
]
=
1
2
x
[
n
]
-
1
4
{
x
[
n
-
T
]
+
x
[
n
+
T
]
}
for inter-harmonic attenuation of the decoded sound signal, where x[n] is the decoded sound signal, y[n] is the inter-harmonic filtered decoded sound signal in a given sub-band, and T is a pitch delay of the decoded sound signal.
17. A post-processing method as defined in claim 16 , further comprising summing the unprocessed decoded sound signal and the inter-harmonic filtered frequency low-band signal to produce an output post-processed decoded sound signal.
18. A post-processing method as defined in claim 1 , wherein pitch enhancing comprises pitch enhancing the decoded sound signal using the following equation:
y
[
n
]
=
(
1
-
α
2
)
x
[
n
]
+
α
4
{
x
[
n
-
T
]
+
x
[
n
+
T
]
}
where x[n] is the decoded sound signal, y[n] is the pitch enhanced decoded sound signal in a given sub-band, T is a pitch delay of the decoded sound signal, and α is a coefficient varying between 0 and 1 to control an amount of inter-harmonic attenuation of the decoded sound signal.
19. A post-processing method as defined in claim 18 , comprising receiving the pitch delay T through a bitstream.
20. A post-processing method as defined in claim 18 , comprising decoding the pitch delay T from a received, encoded bitstream.
21. A post-processing method as defined in claim 18 , comprising calculating the pitch delay T in response to the decoded sound signal for an improved pitch tracking.
22. A post-processing method as defined in claim 1 , wherein, during encoding, the sound signal is down-sampled from a higher sampling frequency to a lower sampling frequency, and wherein dividing the decoded sound signal into a plurality of frequency sub-band signals comprises up-sampling the decoded sound signal from the lower sampling frequency to the higher sampling frequency.
23. A post-processing method as defined in claim 22 , wherein dividing the decoded sound signal into a plurality of frequency sub-band signals comprises sub-band filtering the decoded sound signal, and wherein the up-sampling of the decoded sound signal from the lower sampling frequency to the higher sampling frequency is combined to the sub-band filtering.
24. A post-processing method as defined in claim 22 , comprising:
band-pass filtering the decoded sound signal to produce a frequency upper-band signal, said band-pass filtering of the decoded sound signal being combined with up-sampling of the decoded sound signal from the lower sampling frequency to the higher sampling frequency; and
pitch enhancing the decoded sound signal and low-pass filtering the pitch enhanced decoded sound signal to produce a frequency lower-band signal, said low-pass filtering of the pitch enhanced decoded sound signal being combined with up-sampling of the post-processed decoded sound signal from the lower sampling frequency to the higher sampling frequency.
25. post-processing method as defined in claim 24 , further comprising adding the frequency upper-band signal with the frequency lower-band signal to form an output post-processed and up-sampled decoded sound signal.
26. A post-processing method as defined in claim 24 , wherein pitch enhancing the decoded sound signal comprises processing the decoded sound signal by means of the following equation:
y
[
n
]
=
(
1
-
α
2
)
x
[
n
]
+
α
4
{
x
[
n
-
T
]
+
x
[
n
+
T
]
}
where x[n] is the decoded sound signal, y[n] is the pitch enhanced decoded sound signal in a given sub-band, T is a pitch delay of the decoded sound signal, and α is a coefficient varying between 0 and 1 to control an amount of inter-harmonic attenuation of the decoded sound signal.
27. A post-processing method as defined in claim 1 , wherein:
dividing the decoded sound signal into a plurality of frequency sub-band signals comprises dividing the decoded sound signal into a frequency upper-band signal and a frequency lower-band signal; and
pitch enhancing comprises pitch enhancing the frequency lower-band signal.
28. A post-processing method as defined in claim 1 , wherein pitch enhancing comprises:
determining a pitch value of the decoded sound signal;
calculating, in relation to the determined pitch value, a high-pass filter with a cut-off frequency below a fundamental frequency of the decoded sound signal; and
processing the decoded sound signal through the calculated high-pass filter.
29. A device for post-processing a decoded sound signal in view of enhancing a perceived quality of said decoded sound signal, comprising:
a divider of the decoded sound signal into a plurality of frequency sub-band signals; and
a post-processor of only a part of the frequency sub-band signals;
wherein the post-processor comprises a pitch enhancer of the frequency sub-band signals only in a lower frequency band of the decoded sound signal.
30. A post-processing device as defined in claim 29 , further comprising an adder for summing the frequency sub-band signals, after post-processing of said part of the frequency sub-band signals, to produce an output post-processed decoded sound signal.
31. A post-processing device as defined in claim 29 , wherein the post-processor comprises an adaptive filter supplied with the decoded sound signal.
32. A post-processing device as defined in claim 29 , wherein the divider comprises a sub-band filter supplied with the decoded sound signal.
33. A post-processing device as defined in claim 29 , wherein, for said part of the frequency sub-band signals:
the post-processor comprises an adaptive filter supplied with the decoded sound signal to produce an adaptively filtered decoded sound signal; and
the dividing means comprises a sub-band filter supplied with the adaptively filtered decoded sound signal.
34. A post-processing device as defined in claim 29 , wherein:
the dividing means comprises:
a high-pass filter supplied with the decoded sound signal to produce a frequency high-band signal; and
a first low-pass filter supplied with the decoded sound signal to produce a frequency low-band signal; and
the pitch enhancer enhances the decoded sound signal prior to low-pass filtering the decoded sound signal through the first low-pass filter.
35. A post-processing device as defined in claim 34 , wherein the post-processor further comprises a second low-pass filter supplied with the decoded sound signal to produce a low-pass filtered decoded sound signal supplied to the pitch enhancer.
36. A post-processing device as defined in claim 34 ,further comprising an adder for summing the frequency high-band and low-band signals to produce an output post-processed decoded sound signal.
37. A post-processing device as defined in claim 29 , wherein:
the divider comprises:
a band-pass filter supplied with the decoded sound signal to produce a frequency upper-band signal; and
a low-pass filter supplied with the decoded sound signal to produce a frequency lower-band signal; and
the pitch enhancer enhances the decoded sound signal prior to low-pass filtering the decoded sound signal through the low-pass filter to produce the frequency lower-band signal.
38. A post-processing device as defined in claim 37 , wherein the pitch enhancer comprises a pitch filter supplied with the decoded sound signal to produce a pitch enhanced decoded sound signal supplied to the low-pass filter.
39. A post-processing device as defined in claim 37 , further comprising an adder for summing the frequency upper-band and lower-band signals to produce an output post-processed decoded sound signal.
40. A post-processing device as defined in claim 29 , wherein: the divider comprises:
a low-pass filter supplied with the decoded sound signal to produce a frequency low-band signal; and
the pitch enhancer enhances the decoded sound signal to produce a post-processed pitch enhanced decoded sound signal supplied to the low-pass filter.
41. A post-processing device as defined in claim 40 , wherein the pitch enhancer comprises an inter-harmonic filter supplied with the decoded sound signal to produce an inter-harmonic, attenuated decoded sound signal.
42. A post-processing device as defined in claim 41 , wherein the pitch enhancer comprises a multiplier for multiplying the inter-harmonic, attenuated decoded sound signal by an adaptive pitch enhancement gain.
43. A post-processing device as defined in claim 41 , further comprising a low-pass filter supplied with the decoded sound signal to produce a low-pass filtered decoded sound signal supplied to the inter-harmonic filter.
44. A post-processing device as defined in claim 40 , further comprising an adder for summing the decoded sound signal and the frequency low-band signal to produce an output post-processed decoded sound signal.
45. A post-processing device as defined in claim 40 , wherein the pitch enhancer comprises an inter-harmonic filter having the following transfer function:
y
[
n
]
=
1
2
x
[
n
]
-
1
4
{
x
[
n
-
T
]
+
x
[
n
+
T
]
}
for inter-harmonic attenuating the decoded sound signal, where x[n] is the decoded sound signal, y[n] is the inter-harmonic filtered decoded sound signal in a given sub-band, and T is a pitch delay of the decoded sound signal.
46. A post-processing device as defined in claim 45 , further comprising an adder for summing the unprocessed decoded sound signal and the inter-harmonic filtered frequency low-band signal to produce an output post-processed decoded sound signal.
47. A post-processing device as defined in claim 29 , wherein the pitch enhancer of the decoded sound signal uses the following equation:
y
[
n
]
=
(
1
-
α
2
)
x
[
n
]
+
α
4
{
x
[
n
-
T
]
+
x
[
n
+
T
]
}
where x[n] is the decoded sound signal, y[n] is the pitch enhanced decoded sound signal in a given sub-band, T is a pitch delay of the decoded sound signal, and α is a coefficient varying between 0 and 1 to control an amount of inter-harmonic attenuation of the decoded sound signal.
48. A post-processing device as defined in claim 47 , comprising a receiver of the pitch delay T through a bitstream.
49. A post-processing device as defined in claim 47 , comprising a decoder of the pitch delay T from a received, encoded bitstream.
50. A post-processing device as defined in claim 47 , comprising a calculator of the pitch delay T in response to the decoded sound signal for an improved pitch tracking.
51. A post-processing device as defined in claim 29 , wherein, during encoding, the sound signal is down-sampled from a higher sampling frequency to a lower sampling frequency, and wherein the divider comprises an up-sampler of the decoded sound signal from the lower sampling frequency to the higher sampling frequency.
52. A post-processing device as defined in claim 51 , wherein the divider comprises a sub-band filter supplied with the decoded sound signal, and wherein the up-sampler is combined with the sub-band filter.
53. A post-processing device as defined in claim 51 , wherein:
the pitch enhancer enhances the decoded sound signal; and
the divider comprises:
a band-pass filter supplied with the decoded sound signal to produce a frequency upper-band signal, said band-pass filter being combined with the up-sampler; and
a low-pass filter supplied with the pitch enhanced decoded sound signal to produce a frequency lower-band signal, said low-pass filter being combined with the up-sampler.
54. A post-processing device as defined in claim 53 , further comprising an adder for summing the frequency upper-band signal with the frequency lower-band signal to form an output pitch-enhanced and up-sampled decoded sound signal.
55. A post-processing device as defined in claim 53 , wherein the pitch enhancer uses the following equation:
y
[
n
]
=
(
1
-
α
2
)
x
[
n
]
+
α
4
{
x
[
n
-
T
]
+
x
[
n
+
T
]
}
where x[n] is the decoded sound signal, y[n] is the pitch enhanced decoded sound signal in a given sub-band, T is a pitch delay of the decoded sound signal, and α is a coefficient varying between 0 and 1 to control an amount of inter-harmonic attenuation of the decoded sound signal.
56. A post-processing device as defined in claim 29 , wherein:
the divider divides the decoded sound signal into a frequency upper-band signal and a frequency lower-band signal; and
the pitch enhancer enhances the frequency lower-band signal.
57. A post-processing device as defined in claim 29 , wherein the pitch enhancer:
determines a pitch value of the decoded sound signal;
calculates, in relation to the determined pitch value, a high-pass filter with a cut-off frequency below a fundamental frequency of the decoded sound signal; and
processes the decoded sound signal through the calculated high-pass filter.
58. A sound signal decoder comprising:
an input for receiving an encoded sound signal;
a parameter decoder supplied with the encoded sound signal for decoding sound signal encoding parameters;
a sound signal decoder supplied with the decoded sound signal encoding parameters for producing a decoded sound signal; and
a post-processing device as recited in any of claims 29 to 57 for post-processing the decoded sound signal in view of enhancing a perceived quality of said decoded sound signal.