Spectrum flatness control for bandwidth extension
First Claim
1. A method of decoding an encoded audio bitstream at a decoder, the method comprising:
- receiving, by a processor in the decoder, the audio bitstream from the network, the audio bitstream comprising a low band bitstream;
decoding, by the processor in the decoder, the low band bitstream to get low band coefficients in a frequency domain;
copying, by the processor in the decoder, a plurality of the low band coefficients to a high frequency band location to generate high band coefficients;
evaluating, by the processor in the decoder, modification gains through following equation;
Gain(k)=(C0+C1·
√
{square root over (Mean_HB/F_energy_dec[k])}), k=Start_HB, . . . ,End_HB−
1,wherein {Gain(k), k=Start_HB, . . . , End_HB−
1} are the modification gains, F_energy_dec[k] is an energy distribution at each frequency location index k of a copied high band, Start_HB and End_HB define a high band range, C0 and C1 satisfying C0+C1=1 are pre-determined constants, and Mean_HB is a mean energy value obtained by averaging energies of the high band coefficients;
modifying, by the processor in the decoder, an energy envelope of the high band coefficients to flatten and smooth the high band coefficients by multiplying modification gains with the high band coefficients in the frequency domain to form processed high band coefficients, wherein the processed high band coefficients have an energy closer to the mean energy value;
applying, by the processor in the decoder, a received spectral envelope to the high band coefficients, the received spectral envelope being decoded from the received audio bitstream; and
inverse-transforming, by the processor in the decoder, the low band coefficients and the processed high band coefficients to a time domain to obtain a time domain audio output signal.
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Abstract
In accordance with an embodiment, a method of decoding an encoded audio bitstream at a decoder includes receiving the audio bitstream, decoding a low band bitstream of the audio bitstream to get low band coefficients in a frequency domain, and copying a plurality of the low band coefficients to a high frequency band location to generate high band coefficients. The method further includes processing the high band coefficients to form processed high band coefficients. Processing includes modifying an energy envelope of the high band coefficients by multiplying modification gains to flatten or smooth the high band coefficients, and applying a received spectral envelope decoded from the received audio bitstream to the high band coefficients. The low band coefficients and the processed high band coefficients are then inverse-transformed to the time domain to obtain a time domain output signal.
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Citations
16 Claims
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1. A method of decoding an encoded audio bitstream at a decoder, the method comprising:
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receiving, by a processor in the decoder, the audio bitstream from the network, the audio bitstream comprising a low band bitstream; decoding, by the processor in the decoder, the low band bitstream to get low band coefficients in a frequency domain; copying, by the processor in the decoder, a plurality of the low band coefficients to a high frequency band location to generate high band coefficients; evaluating, by the processor in the decoder, modification gains through following equation;
Gain(k)=(C0+C1·
√
{square root over (Mean_HB/F_energy_dec[k])}), k=Start_HB, . . . ,End_HB−
1,wherein {Gain(k), k=Start_HB, . . . , End_HB−
1} are the modification gains, F_energy_dec[k] is an energy distribution at each frequency location index k of a copied high band, Start_HB and End_HB define a high band range, C0 and C1 satisfying C0+C1=1 are pre-determined constants, and Mean_HB is a mean energy value obtained by averaging energies of the high band coefficients;modifying, by the processor in the decoder, an energy envelope of the high band coefficients to flatten and smooth the high band coefficients by multiplying modification gains with the high band coefficients in the frequency domain to form processed high band coefficients, wherein the processed high band coefficients have an energy closer to the mean energy value; applying, by the processor in the decoder, a received spectral envelope to the high band coefficients, the received spectral envelope being decoded from the received audio bitstream; and inverse-transforming, by the processor in the decoder, the low band coefficients and the processed high band coefficients to a time domain to obtain a time domain audio output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A post-processing method of generating a decoded speech/audio signal at a decoder and improving spectrum flatness of a generated high frequency band, the method comprising:
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generating, by a processor in the decoder, high band coefficients from low band coefficients in a frequency domain using a BandWidth Extension (BWE) high band coefficient generation method; flattening and smoothing, by the processor in the decoder, an energy envelope of the high band coefficients in the frequency domain by multiplying flattening and smoothing gains to the high band coefficients, wherein the flattening and smoothing gains are used to generate an energy of modified high band coefficients being closer to a mean energy value obtained by averaging energies of the high band coefficients, and wherein each of the flattening and smoothing gains is individually calculated by the processor in the decoder based on the mean energy value and a value of a corresponding one of the high band coefficients; shaping and determining, by the processor in the decoder, the energies of the high band coefficients by using a BWE shaping and determining method; and inverse-transforming, by the processor in the decoder, the low band coefficients and the high band coefficients to a time domain to obtain a time domain output speech/audio signal. - View Dependent Claims (9, 10, 11, 12)
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13. A system for receiving an encoded audio signal, comprising:
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a memory storage comprising instructions; and one or more processors in communication with the memory, wherein the one or more processors execute the instructions to; transform a low band portion of the encoded audio signal into frequency domain low band coefficients at an output of a low-band block; generate high band coefficients by copying a plurality of the low band coefficients to a high frequency band location; evaluate modification gains through following equation;
Gain(k)=(C0+C1·
√
{square root over (Mean_HB/F_energy_dec[k])}), k=Start_HB, . . . ,End_HB−
1,wherein {Gain(k), k=Start_HB, . . . , End_HB−
1} are the modification gains, F_energy_dec[k] is an energy distribution at each frequency location index k of a copied high band, Start_HB and End_HB define a high band range, C0 and C1 satisfying C0+C1=1 are pre-determined constants, and Mean_HB is a mean energy value obtained by averaging energies of the high band coefficients;generate shaped high band coefficients by multiplying the modification gains with the high band coefficients in the frequency domain to form processed high band coefficients, wherein the processed high band coefficients have an energy closer to the mean energy value, and apply a received spectral envelope to the high band coefficients, the received spectral envelope being decoded from the encoded audio signal; and produce a time domain audio output signal. - View Dependent Claims (14, 15, 16)
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Specification