Device and method for reducing quantization noise in a time-domain decoder
The present disclosure relates to a device and method for reducing quantization noise in a sound signal contained in a time-domain excitation decoded by a time-domain decoder. A future frame time-domain excitation is evaluated based on the decoded time-domain excitation. A concatenated time-domain excitation is produced from the decoded time-domain excitation of the time-domain excitation of the future frame and is converted into a frequency-domain excitation. A weighting mask is produced for retrieving spectral information lost in the quantization noise. The frequency-domain excitation is modified to increase spectral dynamics by application of the weighting mask. The modified frequency-domain excitation is converted into a modified time-domain excitation. The latter conversion is delay-less. In an embodiment, the weighting mask may be produced using time averaging or frequency averaging or a combination of time and frequency averaging of the frequency-domain excitation. The method and device can be used for improving music content rendering of linear-prediction (LP) based codecs.
1. A device for reducing quantization noise in a sound signal contained in a time-domain excitation decoded by a time-domain decoder, comprising:
at least one processor; and
a memory coupled to the at least one processor and comprising non-transitory code instructions that, when executed, cause the at least one processor to implement:
an excitation extrapolator to evaluate, based on the decoded time-domain excitation, a time-domain excitation of a future frame;
an excitation concatenator to concatenate the decoded time-domain excitation and the extrapolated time-domain excitation of the future frame to form a concatenated time-domain excitation;
a converter of the concatenated time-domain excitation into a frequency-domain excitation;
a mask builder to produce a weighting mask for retrieving spectral information lost in the quantization noise;
a modifier of the frequency-domain excitation to increase spectral dynamics by application of the weighting mask; and
a converter of the modified frequency-domain excitation into a modified time-domain excitation;
wherein conversion of the modified frequency-domain excitation into the modified time-domain excitation is delay-less.
2. A device according to claim 1 , comprising:
a classifier of a synthesis of the decoded time-domain excitation into one of a first set of excitation categories and a second set of excitation categories;
wherein:
the second set of excitation categories comprises INACTIVE or UNVOICED categories; and
the first set of excitation categories comprises an OTHER category.
3. A device according to claim 2 , wherein the converter of the concatenated time-domain excitation into a frequency-domain excitation is applied when the synthesis of the decoded time-domain excitation is classified in the first set of excitation categories.
4. A device according to claim 2 , wherein the classifier of the synthesis of the decoded time-domain excitation into one of a first set of excitation categories and a second set of excitation categories uses classification information transmitted from an encoder to the time-domain decoder and retrieved at the time-domain decoder from a decoded bitstream.
5. A device according to claim 2 , comprising a first synthesis filter to produce a synthesis of the modified time-domain excitation.
6. A device according to claim 5 , comprising a second synthesis filter to produce the synthesis of the decoded time-domain excitation.
7. A device according to claim 5 , comprising a de-emphasizing filter and resampler to generate a sound signal from one of the synthesis of the decoded time-domain excitation and of the synthesis of the modified time-domain excitation.
8. A device according to claim 5 , comprising a two-stage classifier for selecting an output synthesis as:
the synthesis of the decoded time-domain excitation when the synthesis of the decoded time-domain excitation is classified in the second set of excitation categories; and
the synthesis of the modified time-domain excitation when the synthesis of the decoded time-domain excitation is classified in the first set of excitation categories.
9. A device according to claim 1 , comprising an analyzer of the frequency-domain excitation to determine whether the frequency-domain excitation contains music.
10. A device according to claim 9 , wherein the analyzer of the frequency-domain excitation determines that the frequency-domain excitation contains music by comparing a statistical deviation of spectral energy differences of the frequency-domain excitation with a threshold.
11. A device according to claim 1 , wherein the excitation concatenator concatenates past, current and future time-domain excitations.
12. A method for reducing quantization noise in a sound signal contained in a time-domain excitation decoded by a time-domain decoder, comprising:
evaluating, based on the decoded time-domain excitation, a time-domain excitation of a future frame;
concatenating the decoded time-domain excitation and the time-domain excitation of the future frame to form a concatenated time-domain excitation;
converting, by the time-domain decoder, the concatenated time-domain excitation into a frequency-domain excitation;
producing a weighting mask for retrieving spectral information lost in the quantization noise;
modifying the frequency-domain excitation to increase spectral dynamics by application of the weighting mask; and
converting the modified frequency-domain excitation into a modified time-domain excitation;
wherein conversion of the modified frequency-domain excitation into the modified time-domain excitation is delay-less.
13. A method according to claim 12 , comprising:
classifying a synthesis of the decoded time-domain excitation into one of a first set of excitation categories and a second set of excitation categories;
wherein:
the second set of excitation categories comprises INACTIVE or UNVOICED categories; and
the first set of excitation categories comprises an OTHER category.
14. A method according to claim 13 , comprising applying a conversion of the concatenated time-domain excitation into a frequency-domain excitation to the concatenated time-domain excitation classified in the first set of excitation categories.
15. A method according to claim 13 , comprising using classification information transmitted from an encoder to the time-domain decoder and retrieved at the time-domain decoder from a decoded bitstream to classify the synthesis of the decoded time-domain excitation into the one of a first set of excitation categories and a second set of excitation categories.
16. A method according to claim 13 , comprising producing a synthesis of the modified time-domain excitation.
17. A method according to claim 16 , comprising generating a sound signal from one of the synthesis of the decoded time-domain excitation and of the synthesis of the modified time-domain excitation.
18. A method according to claim 16 , comprising selecting an output synthesis as:
the synthesis of the decoded time-domain excitation when the synthesis of the decoded time-domain excitation is classified in the second set of excitation categories; and
the synthesis of the modified time-domain excitation when the synthesis of the decoded synthesis of the decoded time-domain excitation is classified in the first set of excitation categories.
19. A method according to claim 12 , comprising analyzing the frequency-domain excitation to determine whether the frequency-domain excitation contains music.
20. A method according to claim 19 , comprising determining that the frequency-domain excitation contains music by comparing a statistical deviation of spectral energy differences of the frequency-domain excitation with a threshold.
21. A method according to claim 12 , comprising concatenating past, current and extrapolated time-domain excitation excitations.
22. A device for reducing quantization noise in a sound signal contained in a time-domain excitation decoded by a time-domain decoder, comprising:
at least one processor; and
a memory coupled to the at least one processor and comprising non-transitory code instructions that, when executed, cause the at least one processor to:
evaluate, based on the decoded time-domain excitation, a time-domain excitation of a future frame;
concatenate the decoded time-domain excitation and the time-domain excitation of the future frame to form a concatenated time-domain excitation;
convert the concatenated time-domain excitation into a frequency-domain excitation;
produce a weighting mask for retrieving spectral information lost in the quantization noise;
modify the frequency-domain excitation to increase spectral dynamics by application of the weighting mask; and
converting the modified frequency-domain excitation into a modified time-domain excitation;
wherein conversion of the modified frequency-domain excitation into the modified time-domain excitation is delay-less.
23. A device for reducing quantization noise in a sound signal contained in a time-domain excitation decoded by a time-domain decoder, comprising:
an excitation extrapolator to evaluate, based on the decoded time-domain excitation, a time-domain excitation of a future frame;
an excitation concatenator to concatenate the decoded time-domain excitation and the extrapolated time-domain excitation of the future frame to form a concatenated time-domain excitation;
a converter of the concatenated time-domain excitation into a frequency-domain excitation;
a mask builder to produce a weighting mask for retrieving spectral information lost in the quantization noise;
a modifier of the frequency-domain excitation to increase spectral dynamics by application of the weighting mask; and
a converter of the modified frequency-domain excitation into a modified time-domain excitation;
wherein conversion of the modified frequency-domain excitation into the modified time-domain excitation is delay-less.