Estimation of mixing factors to generate high-band excitation signal

• US 10,083,708 B2
• Filed: 10/08/2014
• Issued: 09/25/2018
• Est. Priority Date: 10/11/2013
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Atti, Venkatraman S., Krishnan, Venkatesh
• Primary Examiner(s): Hang, Vu B
• Application Number:
  US14/509,676
• Publication Number:
  US 20150106084A1
• Time in Patent Office: 1,448 Days
• Field of Search: 704201, 704205, 704206, 704219, 704223, 704226, 704227, 704228
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/087 using mixed excitation models, e.g. MELP, MBE, split band LPC or HVXC
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0216 characterised by the method used for estimating noise
• CPC Class Codes: G10L 21/038 using band spreading techniques
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10

Abstract

A method includes generating a high-band residual signal based on a high-band portion of an audio signal. The method also includes generating a harmonically extended signal at least partially based on a low-band portion of the audio signal. The method further includes determining a mixing factor based on the high-band residual signal, the harmonically extended signal, and modulated noise. The modulated noise is at least partially based on the harmonically extended signal and white noise.

Claims

1. A method of adjusting a mixing parameter to reduce artifacts associated with a high-band estimate, the method comprising:

generating, at a speech encoder, a high-band residual signal based on a high-band portion of an audio signal;

generating a harmonically extended signal at least partially based on a low-band portion of the audio signal;

estimating a high-band adjustment factor using a closed-loop analysis, the high-band adjustment factor estimated based on the high-band residual signal, the harmonically extended signal, and modulated noise, wherein the modulated noise is at least partially based on the harmonically extended signal and white noise;

estimating a mixing factor based on the high-band adjustment factor and a voicing factor;

scaling the harmonically extended signal based on the mixing factor to generate a first scaled signal;

scaling the modulated noise based on the mixing factor to generate a second scaled signal;

combining the first scaled signal and the second scaled signal to generate a high-band excitation signal;

generating an encoded bit-stream corresponding to an encoded version of the audio signal, the encoded bit-stream including data representing the high-band adjustment factor; and

transmitting the encoded bit-stream to a receiver, the encoded bit-stream usable by the receiver to reconstruct the audio signal.

2. The method of claim 1, wherein estimating the high-band adjustment factor using the closed-loop analysis comprises:

comparing the high-band residual signal to the high-band excitation signal;

generating an error signal based on the comparison; and

adjusting the high-band adjustment factor based on the error signal.

3. The method of claim 2, wherein the error signal is based on a difference of temporal characteristics of the high-band excitation signal and temporal characteristics of the high-band residual signal.

4. The method of claim 1, wherein the mixing factor is further estimated at least based on low band voicing, low band tilt, or any combination thereof.

5. The method of claim 1, further comprising:

selectively incrementing or decrementing a first high-band adjustment factor to generate a second high-band adjustment factor,

wherein the high-band adjustment factor corresponds to the first high-band adjustment factor in response to a determination that a mean square error based on the first high-band adjustment factor is less than a mean square error based on the second high-band adjustment factor, and

wherein the high-band adjustment factor corresponds to the second high-band adjustment factor in response to a determination that the mean square error based on the second high-band adjustment factor is less than the mean square error based on the first high-band adjustment factor.

6. The method of claim 1, further comprising:

performing a linear predication analysis on the high-band portion of the audio signal to generate the high-band residual signal;

performing a linear prediction analysis on the low-band portion of the audio signal to generate a low-band residual signal;

quantizing the low-band residual signal to generate a low-band excitation signal; and

performing a non-linear filtering operation on the low-band excitation signal to generate the harmonically extended signal.

7. An apparatus for adjusting a mixing parameter to reduce artifacts associated with a high-band estimate, the apparatus comprising:

a linear prediction analysis filter configured to generate a high-band residual signal based on a high-band portion of an audio signal;

a non-linear transformation generator configured to generate a harmonically extended signal at least partially based on a low-band portion of the audio signal;

a high-band adjustment factor calculator configured to estimate a high-band adjustment factor using a closed-loop analysis, the high-band adjustment factor estimated based on the high-band residual signal, the harmonically extended signal, and modulated noise, wherein the modulated noise is at least partially based on the harmonically extended signal and white noise;

a mixing factor calculator configured to estimate a mixing factor based on the high-band adjustment factor and a voicing factor;

a high-band excitation generator configured to;

scale the harmonically extended signal based on the mixing factor to generate a first scaled signal;

scale the modulated noise based on the mixing factor to generate a second scaled signal; and

combine the first scaled signal and the second scaled signal to generate a high-band excitation signal;

encoding circuitry configured to generate an encoded bit-stream corresponding to an encoded version of the audio signal, the encoded bit-stream including data representing the high-band adjustment factor; and

a transmitter configured to transmit the encoded bit-stream to a receiver, the encoded bit-stream usable by the receiver to reconstruct the audio signal.

8. The apparatus of claim 7, further comprising an error detection circuit and an error minimization calculator to estimate the high-band adjustment factor using the closed-loop analysis;

wherein the error detection circuit is configured to compare the high-band residual signal to the high-band excitation signal; and

wherein the error minimization calculator is configured to;

generate an error signal based on the comparison; and

adjust the high-band adjustment factor based on the error signal.

9. The apparatus of claim 8, wherein the error signal is based on a difference of temporal characteristics of the high-band excitation signal and temporal characteristics of the high-band residual signal.

10. The apparatus of claim 7, wherein the mixing factor calculator is further configured to estimate the mixing factor at least based on low band voicing, low band tilt, or any combination thereof.

11. The apparatus of claim 7, further comprising an error controller configured to:

selectively increment or decrement a first high-band adjustment factor to generate a second high-band adjustment factor,

wherein the high-band adjustment factor corresponds to the first high-band adjustment factor in response to a determination that a mean square error based on the first high-band adjustment factor is less than a mean square error based on the second high-band adjustment factor, and

wherein the high-band adjustment factor corresponds to the second high-band adjustment factor in response to a determination that the mean square error based on the second high-band adjustment factor is less than the mean square error based on the first high-band adjustment factor.

12. The apparatus of claim 7,

wherein the linear prediction analysis filter is configured to perform a first linear prediction analysis on the high-band portion of the audio signal to generate the high-band residual signal, and further comprising:

a second linear prediction analysis filter configured to perform a second linear prediction analysis on the low-band portion of the audio signal to generate a low-band residual signal; and

a quantizer configured to quantize the low-band residual signal to generate a low-band excitation signal,

wherein the non-linear transformation generator is configured to perform a non-linear filtering operation on the low-band excitation signal to generate the harmonically extended signal.

13. A non-transitory computer readable medium comprising instructions for adjusting a mixing parameter to reduce artifacts associated with a high-band estimate, the instructions, when executed by a processor at a speech encoder, cause the processor to perform operations comprising:

generating a high-band residual signal based on a high-band portion of an audio signal;

generating a harmonically extended signal at least partially based on a low-band portion of the audio signal;

estimating a high-band adjustment factor using a closed-loop analysis, the high-band adjustment factor estimated based on the high-band residual signal, the harmonically extended signal, and modulated noise, wherein the modulated noise is at least partially based on the harmonically extended signal and white noise;

estimating a mixing factor based on the high-band adjustment factor and a voicing factor;

scaling the harmonically extended signal based on the mixing factor to generate a first scaled signal;

scaling the modulated noise based on the mixing factor to generate a second scaled signal;

combining the first scaled signal and the second scaled signal to generate the high-band excitation signal;

generating an encoded bit-stream corresponding to an encoded version of the audio signal, the encoded bit-stream including data representing the high-band adjustment factor; and

initiating transmission of the encoded bit-stream to a receiver, the encoded bit-stream usable by the receiver to reconstruct the audio signal.

14. The non-transitory computer readable medium of claim 13, wherein estimating the high-band adjustment factor using the closed-loop analysis comprises:

comparing the high-band residual signal to the high-band excitation signal;

generating an error signal based on the comparison; and

adjusting the high-band adjustment factor based on the error signal.

15. The non-transitory computer readable medium of claim 14, wherein the error signal is based on a difference of temporal characteristics of the high-band excitation signal and temporal characteristics of the high-band residual signal.

16. An apparatus for adjusting a mixing parameter to reduce artifacts associated with a high-band estimate, the apparatus comprising:

means for generating a high-band residual signal based on a high-band portion of an audio signal;

means for generating a harmonically extended signal at least partially based on a low-band portion of the audio signal;

means for estimating a high-band adjustment factor using a closed-loop analysis, the high-band adjustment factor estimated based on the high-band residual signal, the harmonically extended signal, and modulated noise, wherein the modulated noise is at least partially based on the harmonically extended signal and white noise;

means for estimating a mixing factor based on the high-band adjustment factor and a voicing factor;

means for generating a high-band excitation signal, the means for generating the high-band excitation signal comprising;

means for scaling the harmonically extended signal based on the mixing factor to generate a first scaled signal;

means for scaling the modulated noise based on the mixing factor to generate a second scaled signal; and

mean for combining the first scaled signal and the second scaled signal to generate the high-band excitation signal;

means for generating an encoded bit-stream corresponding to an encoded version of the audio signal, the encoded bit-stream including data representing the high-band adjustment factor; and

means for transmitting the encoded bit-stream to a receiver, the encoded bit-stream usable by the receiver to reconstruct the audio signal.

17. The apparatus of claim 16, wherein estimating the high-band adjustment factor using the closed-loop analysis comprises:

comparing the high-band residual signal to the high-band excitation signal, wherein the high-band excitation signal is generated based on the high-band adjustment factor, the harmonically extended signal, and the modulated noise;

generating an error signal based on the comparison; and

adjusting the high-band adjustment factor based on the error signal.

18. The apparatus of claim 17, wherein the error signal is based on a difference of temporal characteristics of the high-band excitation signal and temporal characteristics of the high-band residual signal.