AUDIO ENCODING METHOD, AUDIO DECODING METHOD, AUDIO ENCODING DEVICE, AUDIO DECODING DEVICE, PROGRAM, AND AUDIO ENCODING/DECODING SYSTEM

• US 20100106509A1
• Filed: 06/25/2008
• Published: 04/29/2010
• Est. Priority Date: 06/27/2007
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Shimada, Osamu
• Granted Patent: US 8,788,264 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components

Abstract

An audio encoding device (1A) corrects initial gain information calculated for an arbitrary frame, based on gain information of a stored past frame, thereby calculating gain information to be used in the frame. The audio encoding device (1A) encodes the calculated gain information as a difference from the gain information of the past frame. An audio decoding device (3A) receives the differential gain, and calculates the gain of the arbitrary frame based on the gain used in the past frame, thereby generating a decoded audio signal.

Claims

1. An audio encoding method comprising:

the orthogonal transformation step of transforming an input audio signal into a frequency signal for each frame;

the gain calculation step of calculating, for each band including a plurality of frequency signals, a gain for scaling the frequency signal obtained in the orthogonal transformation step, and correcting each gain by using a past gain used in a past frame, thereby calculating a corrected gain;

the quantization step of generating a quantized signal by scaling and quantizing the frequency signal for each band by using the corrected gain obtained in the gain calculation step;

the gain encoding step of generating gain information by encoding, for each band, a difference between the corrected gain obtained in the gain calculation step and the corresponding past gain as the gain information; and

the multiplexing step of generating encoded audio data by multiplexing, for each band, the quantized signal obtained in the quantization step and the gain information obtained in the gain encoding step.

2. An audio encoding method according to claim 1, wherein the gain calculation step comprises the step of calculating the corrected gain based on an evaluation value calculated from an evaluation function calculated from a quantization distortion amount, and an evaluation function calculated from a gain code rate.

3. An audio encoding method according to claim 1, wherein the gain calculation step comprises the step of calculating the corrected gain such that an absolute value of a difference between the past gain and the corrected gain is not more than an absolute value of a difference between the past gain and an initial gain.

4. An audio encoding method according to claim 1, wherein the gain encoding step comprises the step of averaging, for a plurality of bands, differential gains each calculated for each band from a difference between the corrected gain and the past gain, calculating a difference between the obtained average differential value and the differential gain for each band, and encoding the differences and the average differential value as the gain information.

5. An audio encoding method according to claim 1, wherein the gain encoding step comprises the step of using a gain selected from past gains of a predetermined number of previous frames as the past gain, and encoding frame number information of the selected frame.

6. An audio encoding method according to claim 1, wherein the gain calculation step comprises the step of always using a gain of an immediately preceding frame as the past gain.

7. An audio encoding method according to claim 1, wherein

the gain calculation step comprises the step of selecting, based on an uncorrected gain and a corrected gain, one of a time direction and a frequency direction as a direction in which a gain of a frame of interest is to be differentially encoded, and

the gain encoding step comprises the step of differentially encoding the gain in accordance with the differential encoding direction selected in the gain calculation step.

23. A program which causes a computer of an audio encoding device to execute an audio encoding method cited in claim 1.

8. An audio decoding method comprising:

the demultiplexing step of demultiplexing, for each band including a plurality of frequency signals, quantized signal information and gain information for scaling the quantized signal from encoded audio data input frame by frame;

the storage step of storing a gain used in a past frame in a memory for each band;

the gain decoding step of decoding a gain of a frame of interest for each band by using a past frame gain acquired from the memory and a differential gain contained in the gain information demultiplexed in the demultiplexing step;

the inverse quantization step of inversely quantizing and scaling the quantized signal information demultiplexed in the demultiplexing step for each band based on the gain obtained in the gain decoding step, thereby generating a frequency signal; and

the orthogonal transformation step of generating a decoded audio signal by orthogonally transforming the frequency signal obtained in the inverse quantization step.

9. An audio decoding method according to claim 8, wherein

the gain information contains, for each band, frame number information indicating an arbitrary past frame, and a differential gain between a gain of the past frame and a gain of a frame of interest, and

the gain decoding step comprises the step of acquiring, for each band, a gain of a past frame corresponding to the frame number information of the gain information from the memory, and calculating the gain of the frame of interest for each band from the past frame gain and the differential gain of the gain information.

10. An audio decoding method according to claim 8, wherein

the gain information contains, for each band, a differential gain between a gain of an immediately preceding frame and the gain of the frame of interest, and

the gain decoding step comprises the step of calculating the gain of the frame of interest for each band from the gain of the immediately preceding frame acquired for each band from the memory and the differential gain of the gain information.

11. An audio decoding method according to claim 8, wherein

the gain information contains differential method information indicating one of a time-direction differential encoding method and a frequency-direction differential encoding method by which the differential gain of the frame of interest is differentially encoded, and

the gain decoding step comprises the step of calculating the gain in accordance with the differential encoding method corresponding to the differential method information of the gain information.

24. A program which causes a computer of an audio decoding device to execute an audio decoding method cited in claim 8.

12. An audio encoding device comprising:

an orthogonal transformer which transforms an input audio signal into a frequency signal for each frame;

a gain calculator which calculates, for each band including a plurality of frequency signals, a gain for scaling the frequency signal obtained by said orthogonal transformer, and corrects each gain by using a past gain used in a past frame, thereby calculating a corrected gain;

a quantizer which generates a quantized signal by scaling and quantizing the frequency signal for each band by using the corrected gain obtained by said gain calculator;

a gain encoder which generates gain information by encoding, for each band, a difference between the corrected gain obtained by said gain calculator and the corresponding past gain as the gain information; and

a multiplexer which generates encoded audio data by multiplexing, for each band, the quantized signal obtained by said quantizer and the gain information obtained by said gain encoder.

13. An audio encoding device according to claim 12, wherein said gain calculator calculates the corrected gain based on an evaluation value calculated from an evaluation function calculated from a quantization distortion amount, and an evaluation function calculated from a gain code rate.

14. An audio encoding device according to claim 12, wherein said gain calculator calculates the corrected gain such that an absolute value of a difference between the past gain and the corrected gain is not more than an absolute value of a difference between the past gain and an initial gain.

15. An audio encoding device according to claim 12, wherein said gain encoder averages, for a plurality of bands, differential gains each calculated for each band from a difference between the corrected gain and the past gain, calculates a difference between the obtained average differential value and the differential gain for each band, and encodes the differences and the average differential value as the gain information.

16. An audio encoding device according to claim 12, wherein said gain encoder uses a gain selected from past gains of a predetermined number of previous frames as the past gain, and encodes frame number information of the selected frame.

17. An audio encoding device according to claim 12, wherein said gain calculator always uses a gain of an immediately preceding frame as the past gain.

18. An audio encoding device according to claim 12, wherein

said gain calculator selects, based on an uncorrected gain and a corrected gain, one of a time direction and a frequency direction as a direction in which a gain of a frame of interest is to be differentially encoded, and

said gain encoder differentially encodes the gain in accordance with the differential encoding direction selected by said gain calculator.

19. An audio decoding device comprising:

a demultiplexer which demultiplexes, for each band including a plurality of frequency signals, quantized signal information and gain information for scaling the quantized signal from encoded audio data input frame by frame;

a memory which stores a gain used in a past frame for each band;

a gain decoder which decodes a gain of a frame of interest for each band by using a past frame gain acquired from said memory and a differential gain contained in the gain information demultiplexed by said demultiplexer;

an inverse quantizer which inversely quantizes and scales the quantized signal information demultiplexed by said demultiplexer for each band based on the gain obtained by said gain decoder, thereby generating a frequency signal; and

an orthogonal transformer which generates a decoded audio signal by orthogonally transforming the frequency signal obtained by said inverse quantizer.

20. An audio decoding device according to claim 19, wherein

the gain information contains, for each band, frame number information indicating an arbitrary past frame, and a differential gain between a gain of the past frame and a gain of a frame of interest, and

said gain decoder acquires, for each band, a gain of a past frame corresponding to the frame number information of the gain information from said memory, and calculates the gain of the frame of interest for each band from the past frame gain and the differential gain of the gain information.

21. An audio decoding device according to claim 19, wherein

the gain information contains, for each band, a differential gain between a gain of an immediately preceding frame and the gain of the frame of interest, and

said gain decoder calculates the gain of the frame of interest for each band from the gain of the immediately preceding frame acquired for each band from said memory and the differential gain of the gain information.

22. An audio decoding device according to claim 19, wherein

the gain information contains differential method information indicating one of a time-direction differential encoding method and a frequency-direction differential encoding method by which the differential gain of the frame of interest is differentially encoded, and

said gain decoder calculates the gain in accordance with the differential encoding method corresponding to the differential method information of the gain information.

25. An audio encoding/decoding system comprising an audio encoding device which generates encoded audio data by encoding an input audio signal, and an audio decoding device which generates a decoded audio signal by decoding the encoded audio data generated by said audio encoding device,

said audio encoding device comprising:

an orthogonal transformer which transforms an input audio signal into a frequency signal for each frame;

a gain calculator which calculates, for each band including a plurality of frequency signals, a gain for scaling the frequency signal obtained by said orthogonal transformer, and corrects each gain by using a past gain used in a past frame, thereby calculating a corrected gain;

a quantizer which generates a quantized signal by scaling and quantizing the frequency signal for each band by using the corrected gain obtained by said gain calculator;

a gain encoder which generates gain information by encoding, for each band, a difference between the corrected gain obtained by said gain calculator and the corresponding past gain as the gain information; and

a multiplexer which generates encoded audio data by multiplexing, for each band, the quantized signal obtained by said quantizer and the gain information obtained by said gain encoder, and

said audio decoding device comprising;

a demultiplexer which demultiplexes, for each band including a plurality of frequency signals, quantized signal information and gain information for scaling the quantized signal from encoded audio data generated by said audio encoding device and input frame by frame;

a memory which stores a gain used in a past frame for each band;

a gain decoder which decodes a gain of a frame of interest for each band by using a past frame gain acquired from said memory and a differential gain contained in the gain information demultiplexed by said demultiplexer;

an inverse quantizer which inversely quantizes and scales the quantized signal information demultiplexed by said demultiplexer for each band based on the gain obtained by said gain decoder, thereby generating a frequency signal; and

an orthogonal transformer which generates a decoded audio signal by orthogonally transforming the frequency signal obtained by said inverse quantizer.