Time reversed audio subframe error concealment
A method and a decoder device of generating a concealment audio subframe of an audio signal are provided. The method comprises generating frequency spectra on a subframe basis where consecutive subframes of the audio signal have a property that an applied window shape of first subframe of the consecutive subframes is a mirrored version or a time reversed version of a second subframe of the consecutive subframes. Peaks of a signal spectrum of a previously received audio signal are detected for a concealment subframe, and a phase of each of the peaks is estimated. A time reversed phase adjustment is derived based on the estimated phase and applied to the peaks of the signal spectrum to form time reversed phase adjusted peaks.
1. A method of generating a concealment audio subframe of an audio signal in a decoding device, the method comprising:
generating frequency spectra on a subframe basis where a first subframe window of consecutive subframes is a mirrored version or a time reversed version of a second subframe window of the consecutive subframes;
detecting peaks of a signal spectrum of a previously received audio signal on a fractional frequency scale;
estimating a phase of each of the peaks;
deriving a phase adjustment for a time reversed concealment audio subframe based on the estimated phase;
applying the phase adjustment to the peaks of the signal spectrum to form phase adjusted peaks and to form a concealment audio subframe based on the phase adjusted peaks, wherein applying the phase adjustment includes applying a time reversal to the concealment audio subframe; and
generating a synthesized concealment audio subframe based on the concealment audio subframe.
2. The method of claim 1 further comprising:
combining the phase adjusted peaks with a noise spectrum of the signal spectrum to form a combined spectrum for the concealment audio subframe; and
wherein the synthesized concealment audio subframe is further generated based on the combined spectrum.
3. The method of claim 1 , wherein the synthesized concealment audio frame comprises at least two consecutive concealment subframes and wherein deriving the phase adjustment, applying the phase adjustment, applying the time reversal and combining the phase adjusted peaks are performed for a first concealment subframe of the at least two consecutive concealment subframes, the method further comprising:
deriving a phase adjustment to apply to the peaks of the signal spectrum for a second non-time reversed concealment subframe of the at least two consecutive concealment subframes;
applying the phase adjustment to the peaks of the signal spectrum for the second non-time reversed subframe to form non-time reversed phase adjusted peaks;
combining the non-time reversed phase adjusted peaks with a noise spectrum of the signal spectrum to form a combined spectrum for the second concealment subframe; and
generating a second synthesized concealment audio subframe based on the combined spectrum.
4. The method of claim 1 further comprising obtaining the signal spectrum of the previously received audio signal from a memory of the decoding device.
5. The method of claim 1 , wherein applying the time reversal comprises applying a complex conjugate to the phase adjusted peaks.
6. The method of claim 1 further comprising associating each peak of the detected peaks with a number of peak frequency bins representing the peak.
7. The method of claim 6 , wherein for each peak frequency bin of the number of peak frequency bins, one of the time reversed phase adjustment and the non-time reversed phase adjustment is applied to the peak frequency bin.
8. The method of claim 7 further comprising:
populating remaining bins of the signal spectrum using coefficients of the stored signal spectrum, the spectral coefficients retaining a desired property of the signal.
9. The method of claim 8 , wherein the desired property comprises correlation with a second channel in a multichannel decoder system.
10. The method of claim 1 , wherein estimating the phase of each of the peaks comprises:
calculating a phase estimation for the peaks of the time reversed phase adjusted peaks in accordance with:
ϕ
i
=
∠
X
^
mem
(
k
i
)
-
f
frac
(
ϕ
C
+
π
)
f
frac
=
f
i
-
k
i
where ϕ i is an estimated phase at frequency f i , ∠{circumflex over (X)} mem (k i ) is an angle of spectrum {circumflex over (X)} mem of a previously received audio signal at a frequency bin k i , f frac is a rounding error, and ϕ c is a tuning constant.
11. The method of claim 10 , wherein a phase adjustment for the peaks of the time reversed concealment audio subframe is calculated in accordance with:
Δϕ
=
-
2
ϕ
0
-
2
π
f
(
N
step
21
+
N
lost
·
N
)
/
N
,
wherein ϕ is a phase of a peak and f is a frequency of a peak, N lost denotes a number of consecutive lost frames, N denotes a length of a subframe, and N step ′ is a distanced in samples between a starting point of an analysis subframe and concealment subframe.
12. A decoder device configured to generate a concealment audio subframe of an audio signal, the decoder device comprising:
processing circuitry; and
memory operatively coupled with the processing circuitry, wherein the memory includes instructions that when executed by the processing circuitry causes the decoder device to perform operations comprising:
generating frequency spectra on a subframe basis a first subframe window of consecutive subframes is a mirrored version or a time reversed version of a second subframe window of the consecutive subframes;
detecting peaks of a signal spectrum of a previously received audio signal on a fractional frequency scale;
estimating a phase of each of the peaks;
deriving a phase adjustment for a time reversed concealment audio subframe based on the estimated phase;
applying the phase adjustment to the peaks of the signal spectrum to form phase adjusted peaks and to form a concealment audio subframe based on the phase adjusted peaks, wherein applying the phase adjustment includes applying a time reversal to the concealment audio subframe; and
generating a synthesized concealment audio subframe based on the concealment audio subframe.
13. The decoder device of claim 12 further adapted to:
combine the phase adjusted peaks with a noise spectrum of the signal spectrum to form a combined spectrum for the concealment audio subframe; and
wherein the synthesized concealment audio subframe is further generated based on the combined spectrum.
14. The decoder device of claim 12 , wherein the synthesized concealment audio frame comprises at least two consecutive concealment subframes and wherein deriving the phase adjustment, applying the phase adjustment, applying the time reversal and combining the phase adjusted peaks are performed for a first concealment subframe of the at least two consecutive concealment subframes, the decoder device further adapted to:
derive a phase adjustment to apply to the peaks of the signal spectrum for a second non-time reversed concealment subframe of the at least two consecutive concealment subframes;
apply the phase adjustment to the peaks of the signal spectrum for the second non-time reversed subframe to form non-time reversed phase adjusted peaks;
combine the non-time reversed phase adjusted peaks with a noise spectrum of the signal spectrum to form a combined spectrum for the second concealment subframe; and
generate a second synthesized concealment audio subframe based on the combined spectrum.
15. The decoder device of claim 12 further adapted to obtain the signal spectrum of the previously received audio signal from a memory of the decoder device.
16. The decoder device of claim 12 adapted to apply the time reversal by applying a complex conjugate to the phase adjusted peaks.
17. The decoder device of claim 12 further adapted to associate each peak of the detected peaks with a number of peak frequency bins representing the peak.
18. The decoder device of claim 17 further adapted to apply one of the phase adjustment for a time reversed concealment subframe and the phase adjustment for a non-time reversed concealment subframe to each peak frequency bin of the number of peak frequency bins.
19. The decoder device of claim 18 further adapted to:
populate remaining bins of the signal spectrum using coefficients of the stored signal spectrum, the spectral coefficients retaining a desired property of the signal.
20. The decoder device of claim 19 , wherein the desired property comprises correlation with a second channel in a multichannel decoder system.
21. The decoder device of claim 12 adapted to estimate the phase of each of the peaks by calculating a phase estimation for the peaks of the time reversed phase adjusted peaks in accordance with:
ϕ
i
=
∠
X
^
mem
(
k
i
)
-
f
frac
(
ϕ
C
+
π
)
f
frac
=
f
i
-
k
i
where ϕ i is an estimated phase at frequency f i , ∠{circumflex over (X)} mem (k i ) is an angle of spectrum {circumflex over (X)} mem of a previously received audio signal at a frequency bin k i , f frac is a rounding error, and ϕ c is a tuning constant.
22. The decoder device of claim 21 adapted to calculate a phase adjustment for the peaks of the time reversed concealment audio subframe in accordance with:
Δϕ
=
-
2
ϕ
0
-
2
π
f
(
N
step
21
+
N
lost
·
N
)
/
N
,
wherein ϕ is a phase of a peak and f is a frequency of a peak, N lost denotes a number of consecutive lost frames, N denotes a length of a subframe, and N step ′ is a distanced in samples between a starting point of an analysis subframe and concealment subframe.
23. A computer program product comprising a non-transitory storage medium including program code to be executed by processing circuitry of a decoder device configured to operate in a communication network, whereby execution of the program code causes the decoder device to perform operations comprising:
generating frequency spectra on a subframe basis where a first subframe window of consecutive subframes is a mirrored version or a time reversed version of a second subframe window of the consecutive subframes;
detecting peaks of a signal spectrum of a previously received audio signal on a fractional frequency scale;
estimating a phase of each of the peaks;
deriving a phase adjustment for a time reversed concealment audio subframe based on the estimated phase;
applying the phase adjustment to the peaks of the signal spectrum to form phase adjusted peaks and to form a concealment audio subframe based on the phase adjusted peaks, wherein applying the phase adjustment includes applying a time reversal to the concealment audio subframe; and
generating a synthesized concealment audio subframe based on the concealment audio subframe.
24. A method of generating a concealment audio subframe for an audio signal in a decoding device, the method comprising:
generating frequency spectra on a subframe basis where a first subframe window of consecutive subframes is a mirrored version or a time reversed version of a second subframe window of the consecutive subframes;
storing a signal spectrum corresponding to a second subframe window of a first two consecutive subframes;
receiving a bad frame indicator for a second two consecutive subframes;
obtaining the signal spectrum;
detecting peaks of the signal spectrum on a fractional frequency scale;
estimating a phase of each of the peaks;
deriving a phase adjustment for a time reversed concealment audio subframe based on the phase estimated;
applying the phase adjustment to the peaks of the signal spectrum to form phase adjusted peaks and to form a concealment audio subframe based on the phase adjusted peaks, wherein applying the phase adjustment includes applying a time reversal to the concealment audio subframe;
combining the phase adjusted peaks with a noise spectrum of the signal spectrum to form a combined spectrum for the first subframe window of the second two consecutive subframes; and
generating a synthesized concealment audio subframe based on the combined spectrum.
25. A decoder device configured to generate a concealment audio subframe of an audio signal, the decoder device comprising:
processing circuitry; and
memory operatively coupled with the processing circuitry, wherein the memory includes instructions that when executed by the processing circuitry causes the decoder device to perform operations comprising:
generating frequency spectra on a subframe basis where a first subframe window of the consecutive subframes is a mirrored version or a time reversed version of a second subframe window of the consecutive subframes;
storing a signal spectrum corresponding to a second subframe window of a first two consecutive subframes;
receiving a bad frame indicator for a second two consecutive subframes;
obtaining the signal spectrum;
detecting peaks of the signal spectrum on a fractional frequency scale;
estimating a phase of each of the peaks;
deriving a phase adjustment for a time reversed concealment audio subframe based on the phase estimated;
applying the phase adjustment to the peaks of the signal spectrum to form phase adjusted peaks and to form a concealment audio subframe based on the phase adjusted peaks, wherein applying the phase adjustment includes applying a time reversal to the concealment audio subframe;
combining the phase adjusted peaks with a noise spectrum of the signal spectrum to form a combined spectrum for the first subframe window of the second two consecutive subframes; and
generating a synthesized concealment audio subframe based on the combined spectrum.
26. A computer program product comprising a non-transitory storage medium including program code to be executed by processing circuitry of a decoder device configured to operate in a communication network, whereby execution of the program code causes the decoder device to perform operations comprising:
generating frequency spectra on a subframe basis where a first subframe of the consecutive subframes is a mirrored version or a time reversed version of a second subframe window of the consecutive subframes;
storing a signal spectrum corresponding to a second subframe window of a first two consecutive subframes;
receiving a bad frame indicator for a second two consecutive subframes;
obtaining the signal spectrum;
detecting peaks of the signal spectrum on a fractional frequency scale;
estimating a phase of each of the peaks;
deriving a phase adjustment for a time reversed concealment audio subframe based on the phase estimated;
applying the phase adjustment to the peaks of the signal spectrum to form phase adjusted peaks and to form a concealment audio subframe based on the phase adjusted peaks, wherein applying the phase adjustment includes applying a time reversal to the concealment audio subframe;
combining the phase adjusted peaks with a noise spectrum of the signal spectrum to form a combined spectrum for the first subframe window of the second two consecutive subframes; and
generating a synthesized concealment audio subframe based on the combined spectrum.