High-band speech coding apparatus and high-band speech decoding apparatus in wide-band speech coding/decoding system and high-band speech coding and decoding method performed by the apparatuses

• US 20060149538A1
• Filed: 11/23/2005
• Published: 07/06/2006
• Est. Priority Date: 12/31/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Kangeun, Son, Changyong, Shin, Jaehyun, Ahn, Youngwook, Kim, Jonghun, Jung, Kyuhyuk, Lee, Insung
• Granted Patent: US 7,801,733 B2
• Time in Patent Office: Days
• US Class Current: 704/219
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

A high-band speech encoding apparatus and a high-band speech decoding apparatus that can reproduce high quality sound even at a low bitrate when wideband speech encoding and decoding using a bandwidth extension function, and a high-band speech encoding and decoding method performed by the apparatuses. The high-band speech encoding apparatus includes: a first encoding unit encoding a high-band speech signal based on a structure in which a harmonic structure and a stochastic structure are combined, if the high-band speech signal has a harmonic component; and a second encoding unit encoding a high-band speech signal based on a stochastic structure if the high-band speech signal has no harmonic components. The high-band speech decoding apparatus includes: a first decoding unit decoding a high-band speech signal based on a combination of a harmonic structure and a stochastic structure using received first decoding information; a second decoding unit decoding the high-band speech signal based on a stochastic structure using received second decoding information; and a switch outputting one of the decoded high-band speech signals received from the first and second decoding units according to received mode selection information.

Claims

1. A high-band speech encoding apparatus in a wideband speech encoding system, the apparatus comprising:

a first encoding unit encoding a high-band speech signal based on a structure in which a harmonic structure and a stochastic structure are combined, when the high-band speech signal has a harmonic component; and

a second encoding unit encoding a high-band speech signal based on a stochastic structure when the high-band speech signal has no harmonic components.

2. The high-band speech encoding apparatus of claim 1, wherein the first encoding unit includes:

a harmonic structure to generate an excitation signal by searching for an amplitude and a phase of a sine wave dictionary for the high-band speech signal using a matching pursuit algorithm; and

a stochastic structure to perform an open loop stochastic codebook search and a closed loop stochastic codebook search using the excitation signal produced using the harmonic structure as a target signal.

3. The high-band speech encoding apparatus of claim 2, wherein the high-band speech signal is a perceptually weighted zero-state high-band speech signal.

4. The high-band speech encoding apparatus of claim 3, wherein the harmonic structure comprises:

a first perceptually weighted inverse-synthesis filter generating an ideal linear prediction residual signal from the perceptually weighted zero-state high-band speech signal;

a searcher using the ideal linear prediction residual signal as the target signal to search for an amplitude and phase of a sine wave dictionary using the matching pursuit algorithm;

a first quantizer quantizing a vector of the sine wave amplitude found by the searcher;

a second quantizer quantizing a vector of the sine wave phase found by the searcher;

a synthesized excitation signal generator generating a synthesized excitation signal based on the quantized sine wave amplitude vector output by the first quantizer and the quantized sine wave phase vector output by the second quantizer;

a third quantizer quantizing a sine wave amplitude normalization factor output by the first quantizer;

a multiplier multiplying the synthesized excitation signal output by the quantized sine wave amplitude normalization factor output from the third quantizer;

a perceptually weighted synthesis filter outputting a synthesis signal obtained by convoluting an impulse response with a signal output by the multiplier; and

a subtractor outputting a residual signal equal to the difference between the perceptually weighted zero-state high-band speech signal and the synthesis signal output by the perceptually weighted synthesis filter.

5. The high-band speech encoding apparatus of claim 4, wherein the searcher obtains an angular frequency of the sine wave dictionary using a pitch value of a low-band speech signal corresponding to the perceptually weighted zero-state high-band speech signal and searches for the amplitude and phase of the sine wave dictionary using the angular frequency.

6. The high-band speech encoding apparatus of claim 4, wherein the first quantizer comprises:

a normalizer normalizing the sine wave dictionary amplitude vector and transmitting the sine wave amplitude normalization factor to the third quantizer;

a modulated discrete cosine transform (MDCT) unit outputting discrete cosine transform coefficients obtained by performing MDCT on the sine wave dictionary amplitude vector normalized by the normalizer;

a coefficient vector quantizer quantizing the discrete cosine transform coefficients output by the MDCT unit and outputting at least one candidate discrete cosine transform coefficient;

an inverse modulated discrete cosine transform (IMDCT) unit outputting a quantized sine wave amplitude vector by performing an inverse modulated descrite cosine transformation on the at least one candidate discrete cosine transform coefficient output by the coefficient vector quantizer;

a subtractor detecting a residual amplitude vector between the normalized sine wave dictionary amplitude vector output by the normalizer and the quantized sine wave amplitude vector output by the IMDCT unit;

a residual amplitude quantizer quantizing the residual amplitude vector output by the subtractor;

an adder adding the quantized residual amplitude vector output by the residual amplitude quantizer to the quantized sine wave amplitude vector output by the IMDCT unit; and

an optimal vector selector selecting one of the quantized sine wave dictionary amplitude vectors output by the adder using the original sine wave dictionary amplitude vector as an optimal sine wave dictionary amplitude vector, the selected optimal sine wave dictionary amplitude vector being most similar to the original sine wave dictionary amplitude vector.

7. The high-band speech encoding apparatus of claim 4, wherein the first quantizer outputs a sine wave dictionary amplitude index as decoding information used to decode the high-band speech signal, and the second quantizer outputs a sine wave dictionary phase index as decoding information used to decode the high-band speech signal.

8. The high-band speech encoding apparatus of claim 4, wherein the stochastic structure comprises:

a second perceptually weighted inverse-synthesis filter producing an ideal excitation signal by convoluting the residual signal output by the subtractor with an impulse response;

an open loop stochastic codebook searcher selecting at least one candidate stochastic codebook from a stochastic codebook by using the ideal excitation signal output by the second perceptually weighted inverse-synthesis filter as the target signal; and

a closed loop stochastic codebook searcher selecting one of the at least one candidate stochastic codebooks using the residual signal output by the subtractor and transmitting a gain of the selected candidate stochastic codebook to the third quantizer,

the third quantizer 2-dimensionally vector quantizes the sine wave amplitude normalization factor and the gain output by the closed loop stochastic codebook searcher and outputs the quantized gain as a gain index, the gain index being the decoding information used to decode the high-band speech signal.

9. The high-band speech encoding apparatus of claim 8, wherein the closed loop stochastic codebook searcher produces a speech level signal by convoluting the impulse response of the perceptually weighted synthesis filter with the at least one candidate stochastic codebook, obtains a mean squared error for the at least one candidate stochastic codebook using a gain between the speech level signal and the residual signal output by the subtractor, the speech level signal, and the residual signal, and selects the stochastic codebook having the smallest mean squared error.

10. The high-band speech encoding apparatus of claim 1, wherein the second encoding unit comprises:

a first searcher selecting at least one candidate stochastic codebook for the high-band speech signal;

a second searcher selecting an optimal candidate stochastic codebook from the at least one candidate stochastic codebook selected by the first searcher and producing an index for the selected optimal candidate stochastic codebook, wherein the index for the selected optimal candidate stochastic codebook is decoding information necessary for decoding the encoded high-band speech signal.

11. The high-band speech encoding apparatus of claim 10, wherein the high-band speech signal is a perceptually weighted zero-state high-band speech signal.

12. The high-band speech encoding apparatus of claim 11, wherein the second encoding unit further comprises:

a perceptually weighted inverse-synthesis filter producing an ideal excitation signal by convoluting the perceptually weighted zero-state high-band speech signal with an impulse response, and transmitting the ideal excitation signal to the first searcher;

a stochastic codebook including a plurality of stochastic codebooks and outputting the at least one candidate stochastic codebook selected by the first searcher and the optimal candidate stochastic codebook selected by the second searcher;

a multiplier multiplying the at least one stochastic codebook output by the stochastic codebook by the gain received by the second searcher;

a perceptually weighted synthesis filter generating a synthesized signal by convoluting an impulse response with a signal output by the multiplier;

a subtractor outputting a difference between the synthesized signal output by the perceptually weighted synthesis filter and the perceptually weighted zero-state high-band speech signal; and

a gain quantizer quantizing a gain output by the second searcher and outputting the quantized gain as a gain index, the gain index being decoding information necessary for decoding the encoded high-band speech signal.

13. The high-band speech encoding apparatus of claim 1, wherein a determination of whether the high-band speech signal has a harmonic component is made based on a sharpness rate, a left-to-right energy ratio, a zero-crossing rate, and a first-order prediction coefficient of each sub-frame of the high-band speech signal.

14. The high-band speech encoding apparatus of claim 1, further comprising:

a switch transmitting the high-band speech signal to either the first encoding unit or second encoding unit; and

a mode selection unit determining whether the high-band speech signal has a harmonic component and outputting mode selection information for controlling the switch according to a result of the determination.

15. The high-band speech encoding apparatus of claim 14, wherein the mode selection unit detects the sharpness rate, the left-to-right energy ratio, the zero-crossing rate, and the first-order prediction coefficient of each sub-frame of the high-band speech signal, compares the detected sharpness rate, the left-to-right energy ratio, the zero-crossing rate, and the first-order prediction coefficient of each sub-frame of the high-band speech signal with pre-set threshold values, determining that the high-band speech signal has a harmonic component when a result of the comparison satisfies a pre-set condition, and determining that the high-band speech signal has no harmonic components when the result of the comparison does not satisfy the pre-set condition.

16. The high-band speech encoding apparatus of claim 14, wherein the mode selection unit further determines whether a low-band speech signal corresponding to the high-band speech signal has a harmonic component, and controls the switch to transmit the high-band speech signal to the first encoding unit when it is determined that both the high-band speech signal and the low-band speech signal have harmonic components.

17. The high-band speech encoding apparatus of claim 16, wherein the mode selection unit detects the sharpness rate, the left-to-right energy ratio, the zero-crossing rate, and the first-order prediction coefficient of each sub-frame of each of the high-band speech signal and the low-band speech signal, compares the detected sharpness rate, the left-to-right energy ratio, the zero-crossing rate, and the first-order prediction coefficient of each sub-frame of each of the high-band speech signal and the low-band speech signal with pre-set threshold values, determining that both the high-band speech signal and the low-band speech signal have harmonic components when results of the comparisons for the high-band and low-band speech signals satisfy pre-set conditions, and outputs mode selection information that makes the switch to transmit the high-band speech signal to the second encoding unit when at least one of the results of the comparisons does not satisfy the pre-set condition.

18. The high-band speech encoding apparatus of claim 17, wherein the high-band speech signal is a perceptually weighted zero-state high-band speech signal.

19. The high-band speech encoding apparatus of claim 18, further comprising a production unit producing the perceptually weighted zero-state high-band speech signal.

20. The high-band speech encoding apparatus of claim 19, wherein the production unit comprises:

a linear prediction coefficient analyzer obtaining linear prediction coefficients from a high-band speech signal;

a quantizer quantizing the linear prediction coefficients output by the linear prediction coefficient analyzer;

a perceptually weighted synthesis filter outputting a response signal for an input “

0”

according to the quantized linear prediction coefficients output by the quantizer;

a perceptual weighting filter outputting a perceptually weighted speech signal of the high-band speech signal using the linear prediction coefficients obtained by the linear prediction coefficient analyzer; and

a subtractor outputting the perceptually weighted zero-state high-band speech signal by removing the response signal for the input “

0”

received from the perceptually weighted speech signal output by the perceptual weighting filter.

21. The high-band speech encoding apparatus of claim 2, further comprising a production unit producing the perceptually weighted zero-state high-band speech signal.

22. A wideband speech encoding system comprising:

a band division unit dividing a speech signal into a high-band speech signal and a low-band speech signal;

a low-band speech signal encoding apparatus encoding the low-band speech signal received from the band division unit and outputting a pitch value of the low-band speech signal that is detected through the encoding; and

a high-band speech signal encoding apparatus encoding the high-band speech signal using the high-band and low-band speech signals received from the band division unit and the pitch value of the low-band speech signal.

23. The wideband speech encoding system of claim 22, wherein the high-band speech signal encoding apparatus encodes the high-band speech signal based on a combination of a harmonic structure and a stochastic structure when the high-band and low-band speech signals have harmonic components and encodes the high-band speech signal based on a stochastic structure when any one of the high-band and low-band speech signals does not have a harmonic component.

24. A high-band speech decoding apparatus comprising:

a first decoding unit decoding a high-band speech signal based on a combination of a harmonic structure and a stochastic structure using received first decoding information;

a second decoding unit decoding the high-band speech signal based on a stochastic structure using received second decoding information; and

a switch outputting one of the decoded high-band speech signals received from the first and second decoding units according to received mode selection information.

25. The high-band speech decoding apparatus of claim 24, wherein the first decoding information includes a sine wave dictionary amplitude index, a sine wave dictionary phase index, and a stochastic codebook index, and the second decoding information includes a stochastic codebook index and a gain index.

26. The high-band speech decoding apparatus of claim 25, further comprising a linear prediction coefficient dequantization unit obtaining quantized linear prediction coefficients by dequantizing a received linear prediction coefficient index and transmitting the quantized linear prediction coefficients to the first and second decoding units.

27. The high-band speech decoding apparatus of claim 24, further comprising a linear prediction coefficient dequantization unit obtaining quantized linear prediction coefficients by dequantizing a received linear prediction coefficient index and transmitting the quantized linear prediction coefficients to the first and second decoding units.

28. The high-band speech decoding apparatus of claim 25, wherein the first decoding unit comprises:

a gain dequantizer dequantizing the gain index and outputting a quantized gain;

a sine wave amplitude decoder decoding the sine wave dictionary amplitude index to output a quantized sine wave dictionary amplitude vector;

a sine wave phase decoder decoding the sine wave dictionary phase index to output a quantized sine wave dictionary phase vector;

a stochastic codebook outputting a stochastic codebook corresponding to the stochastic codebook index;

a first multiplier multiplying the quantized gain by the quantized sine wave dictionary amplitude vector;

a second multiplier multiplying the quantized gain by the stochastic codebook to produce an excitation signal;

a harmonic signal reconstructor reconstructing a harmonic signal using a signal output by the first multiplier and the quantized sine wave dictionary amplitude vector;

an adder adding the harmonic signal output by the harmonic signal reconstructor to the excitation signal output by the second multiplier; and

a synthesis filter synthesis-filtering a signal output by the adder using the linear prediction coefficients to output the decoded high-band speech signal.

29. The high-band speech decoding apparatus of claim 25, wherein the second decoding unit comprises:

a stochastic codebook receiving the stochastic codebook index and outputting a stochastic codebook corresponding to the stochastic codebook index;

a gain dequantizer receiving the gain index and dequantizing the gain index to output a quantized gain;

a multiplier multiplying the quantized gain by the stochastic codebook to produce an excitation signal; and

a synthesis filter synthesis-filtering a signal output by the multiplier using the linear prediction coefficients.

30. A wideband speech decoding system comprising:

a high-band speech signal decoding apparatus decoding a high-band speech signal using decoding information received via a channel using one of a stochastic structure and a combination of a harmonic structure and the stochastic structure;

a low-band speech signal decoding apparatus decoding a low-band speech signal using decoding information received via the channel; and

a band combination unit combining the decoded high-band speech signal with the decoded low-band speech signal to output a decoded speech signal.

31. A high-band speech encoding method in a wideband speech encoding system, comprising:

determining whether a high-band speech signal and a low-band speech signal have harmonic components;

encoding the high-band speech signal based on a combination of a harmonic structure and a stochastic structure when both the high-band and low-band speech signals have harmonic components; and

encoding the high-band speech signal based on a stochastic structure when any one of the high-band and low-band speech signals does not have a harmonic component.

32. The high-band speech encoding method of claim 31, wherein the determining whether the high-band speech signal and the low-band speech signal have harmonic components comprises:

detecting characteristic values of each of a plurality of subframes of which the high-band and low-band speech signals are comprised;

comparing the detected characteristic values with pre-set threshold values;

determining that a corresponding speech signal has a harmonic component when a result of the comparison satisfies a predetermined condition; and

determining that a corresponding speech signal does not have a harmonic component when the result of the comparison does not satisfy a predetermined condition.

33. The high-band speech encoding method of claim 32, wherein the characteristic values include a sharpness rate, a left-to-right energy ratio, a zero-crossing rate, and a first-order prediction coefficient, and the pre-set threshold values include threshold values of the characteristic values.

34. The high-band speech encoding method of claim 33, wherein the high-band speech signal is a perceptually weighted zero-state high-band speech signal.

35. The high-band speech encoding method of claim 31, wherein the high-band speech signal is a perceptually weighted zero-state high-band speech signal.

36. The high-band speech encoding method of claim 31, wherein the harmonic structure produces an exciting signal by searching for an amplitude and phase of a sine wave dictionary for the high-band speech signal according to a matching pursuit algorithm.

37. A high-band speech decoding method, comprising:

analyzing mode selection information included in received decoding information;

decoding a high-band speech signal based on the received decoding information using a combination of a harmonic structure and a stochastic structure when the mode selection information represents a mode in which a harmonic structure and a stochastic structure are combined; and

decoding the high-band speech signal based on the received decoding information using a stochastic structure when the mode selection information represents a stochastic structure.