METHOD AND DEVICE FOR CLIPPING CONTROL

• US 20120095580A1
• Filed: 12/22/2011
• Published: 04/19/2012
• Est. Priority Date: 06/25/2009
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: ZHANG, Deming
• Granted Patent: US 8,862,257 B2
• Time in Patent Office: Days
• US Class Current: 700/94
• CPC Class Codes: G10L 21/02 Speech enhancement, e.g. noise reduction or echo cancellation reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08
• CPC Class Codes: H04L 25/03828 Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties partial response systems H04L25/497

Abstract

A method and a device for clipping control are provided in the present invention. The method includes: updating a clipping factor according to a maximum absolute value FrameLev in a current frame signal; obtaining a clipping restoration filter according to the clipping factor; filtering the current frame signal according to the clipping restoration filter to obtain a filtered clipping restoration signal. With the method and device for clipping control provided in the present invention, whether a clipping phenomenon occurs may be automatically detected, and clipping restoration is performed, so that subjective quality of an output signal is improved.

Claims

1. A method for clipping control, comprising:

updating a clipping factor according to a maximum absolute value FrameLev in a current frame signal;

obtaining a clipping restoration filter according to the clipping factor; and

filtering the current frame signal according to the clipping restoration filter to obtain a filtered clipping restoration signal.

2. The method for clipping control according to claim 1, wherein the method further comprises:

calculating an automatic gain control factor according to the clipping factor; and

performing gain adjustment on the clipping restoration signal according to the automatic gain control factor to obtain an output signal.

3. The method for clipping control according to claim 1, wherein the updating the clipping factor according to the maximum absolute value FrameLev in the current frame signal comprises:

FrameLev>

THR1, increasing a clipping factor C according to C_k=C_k-1+β

₁;

or,

THR1>

=FrameLev>

THR2, decreasing the clipping factor C according to C_k=C_k-1−

β

₂;

or,

THR2>

=FrameLev>

THR3, decreasing the clipping factor C according to C_k=C_k-1−

β

₁;

or,

THR3>

=FrameLev, keeping the clipping factor C unchanged, C_k=C_k-1;

wherein THR1, THR2 and THR3 are used for representing amplitude intervals of a signal, wherein −

2^x<

=THR3<

THR2<

THR1<

=, and x is the number of bits of a signal processing system, β

₁, β

₂, and β

₃ are used for representing update speeds of a clipping factor C, 0≦

β

₂≦

β

₃≦

β

₁≦

1, C_k is the clipping factor of the current frame signal, and C_k-1 is a clipping factor of a previous frame signal.

4. The method for clipping control according to claim 3, wherein after the updating the clipping factor according to the maximum absolute value FrameLev in the current frame signal, further comprising:

the clipping factor of the current frame signal within an interval [0, 1].

5. The method for clipping control according to claim 1, wherein when the clipping restoration filter is a 1-order all-pass filter, a state function of the clipping restoration filter is:

6. The method for clipping control according to claim 5, wherein the filtering the current frame signal according to the clipping restoration filter to obtain the filtered clipping restoration signal comprises:

s_k′

(i)=−

η

_k×

s_k(i)+y_k-1

y_k=s_k(i)+η

_k×

s_k′

(i)

wherein s_k(i) is a current frame signal of an input signal, s_k′

(i) is a filtered restoration signal obtained by filtering the current frame signal, and y_k is an intermediate variable in a filtering process.

7. The method for clipping control according to claim 2, wherein the calculating the automatic gain control factor according to the clipping factor is specifically:

8. The method for clipping control according to claim 2, wherein the performing gain adjustment on the clipping restoration signal according to the automatic gain control factor to obtain the output signal comprises:

interpolating, according to an automatic gain control factor g_k-1 of a previous frame signal and an automatic gain control factor g_k of the current frame signal, to obtain a gain control curve G{g(i)}; and

performing gain adjustment on the clipping restoration signal to obtain the output signal;

s″

(i)=s′

(i)×

g(i),

wherein, s_k′

(i) is a filtered restoration signal obtained by filtering the current frame signal, and s″

(i) is an output signal after gain adjustment.

9. The method for clipping control according to claim 8, wherein the interpolating, according to the automatic gain control factor g_k-1 of the previous frame signal and the automatic gain control factor g_k, of the current frame signal, to obtain the gain control curve G{g(i)} comprises:

obtaining the gain control curve G{g(i)} by using linear interpolation according to the automatic gain control factor g_k-1 of the previous frame signal and the automatic gain control factor g_k of the current frame signal.

10. The method for clipping control according to claim 9, wherein the obtaining the gain control curve G{g(i)} by using the linear interpolation according to the automatic gain control factor g_k-1 of the previous frame signal and the automatic gain control factor g_k of the current frame signal is specifically:

11. A device for clipping control, comprising:

a clipping factor updating unit, configured to update a clipping factor according to a maximum absolute value FrameLev in a current frame signal;

a clipping restoration filter obtaining unit, configured to obtain a clipping restoration filter according to the clipping factor; and

a filter unit, configured to filter the current frame signal according to the clipping restoration filter to obtain a filtered clipping restoration signal.

12. The device for clipping control according to claim 11, further comprising:

an automatic gain control factor calculation unit, configured to calculate an automatic gain control factor according to the clipping factor; and

a gain adjustment unit, configured to perform gain adjustment on the clipping restoration signal according to the automatic gain control factor to obtain an output signal.

13. The device according to claim 11, wherein,

FrameLev>

THR1, the clipping factor updating unit is specifically configured to rapidly increase a clipping factor C according to C_k=C_k-1+β

₁;

or,

THR1>

=FrameLev>

THR2, the clipping factor updating unit is specifically configured to slowly decrease the clipping factor C according to C_k=C_k-1−

β

₂;

or,

THR2>

=FrameLev>

THR3, the clipping factor updating unit is specifically configured to rapidly decrease the clipping factor C according to C_k=C_k-1−

β

₃;

or,

THR3>

=FrameLev, the clipping factor updating unit is specifically configured to keep the clipping factor C unchanged, C_k=C_k-1;

wherein THR1, THR2 and THR3 are used for representing amplitude intervals of a signal, wherein −

2^x<

=THR3<

THR2<

THR1<

=2^x, x is the number of bits of a signal processing system, β

₁, β

₂, and β

₃ are used for representing update speeds of the clipping factor C, 0≦

β

₂≦

β

₂≦

β

₃<

β

₁≦

1, C_k is the clipping factor of the current frame signal, and C_k-1 is a clipping factor of a previous frame signal.

14. The device for clipping control according to claim 13, further comprising:

a regulating unit, configured to regulate the clipping factor of the current frame signal output by the clipping factor updating unit within an interval [0, 1].

15. The device for clipping control according to claim 11, wherein when the clipping restoration filter is a 1-order all-pass filter, the clipping restoration filter obtaining unit is specifically configured to obtain a state function of the 1-order all-pass filter:

16. The device for clipping control according to claim 15, wherein the filter unit is specifically configured to filter the current frame signal according to the following expressions to obtain the filtered clipping restoration signal:

s_k′

(i)=−

η

_k×

s_k(i)+y_k-1

y_k=s_k(i)+η

_k×

s_k′

(i)

wherein s_k(i) is a current frame signal of an input signal, s_k′

(i) is a filtered restoration signal obtained by filtering the current frame signal, and y_k is an intermediate variable in a filtering process.

17. The device for clipping control according to claim 12, wherein the automatic gain control factor calculation unit calculates the automatic gain control factor according to the following expression:

18. The device for clipping control according to claim 17, wherein the gain adjustment unit is specifically configured to interpolate, according to the automatic gain control factor of the previous frame signal g_k-1 and the automatic gain control factor of the current frame signal g_k, to obtain a gain control curve G{g(i)}, and perform gain adjustment on the clipping restoration signal to obtain an output signal:

s″

(i)=s′

(i)×

g(i),

wherein s_k′

(i) is a filtered restoration signal obtained by filtering the current frame signal, and s″

(i) is an output signal after gain adjustment.

19. The device for clipping control according to claim 18, wherein the gain adjustment unit is specifically configured to obtain the gain control curve G{g(i)} by using linear interpolation according to the automatic gain control factor g_k-1 of the previous frame signal and the automatic gain control factor g_k of the current frame signal.