Audio signal processing device for noise reduction and audio enhancement, and method for the same

• US 8,355,908 B2
• Filed: 03/19/2009
• Issued: 01/15/2013
• Est. Priority Date: 03/24/2008
• Status: Active Grant

• Current Assignee: JVC Kenwood Corporation
• Original Assignee: JVC Kenwood Corporation
• Inventors: Yamabe, Takaaki, Konishi, Masaya
• Primary Examiner(s): Opsasnick, Michael N
• Application Number:
  US12/452,795
• Publication Number:
  US 20100128882A1
• Time in Patent Office: 1,398 Days
• Field of Search: 704224-228
• US Class Current: 704/224
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain
• CPC Class Codes: H03G 3/3005 in amplifiers suitable for low-frequencies, e.g. audio amplifiers H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H03G 3/3089 Control of digital or coded signals
• CPC Class Codes: H04R 2225/43 Signal processing in hearing aids to enhance the speech intelligibility
• CPC Class Codes: H04R 2460/01 Hearing devices using active noise cancellation
• CPC Class Codes: H04R 25/356 Amplitude, e.g. amplitude shift or compression
• CPC Class Codes: H04R 25/505 using digital signal processing

Abstract

In frequency signals obtained by converting input audio signals from time-domain signals to frequency-domain signals, a level control value setting unit 5 establishes a level control value for reducing the levels of spectrums at a noise-components level. A level control value smoothing unit 6 carries out a smoothing process of smoothing the level control value established by the level control value setting unit 5 temporally. A spectral adjustment unit 8 multiplies the level control value after the smoothing process by the frequency signals, performing a level control.

Claims

1. An audio signal processing device comprising:

a frame division unit dividing inputted audio signals into frames as predetermined units;

a frequency converter converting the audio signals on a frame-to-frame basis from time-domain signals to frequency signals as frequency-domain signals;

a level detector detecting respective levels of spectrums of respective frequencies from the frequency signals with respect to each frame;

a level control value setting unit executing a reduction amount setting process of setting a level control value for reducing the levels of the spectrums having levels within a level range between a first threshold value and a second threshold value set lower than the first threshold value, with respect to each frame; and

the level control value setting unit executing an amplification amount setting process of setting a level control value for increasing the level of a spectrum in a predetermined frequency band having a level within a range between a third threshold value set more than the first threshold value and a fourth threshold value set more than the first threshold value and less than the third threshold value, with respect to each frame;

a level control value smoothing unit executing a smoothing process of temporally smoothing a difference between one level control value set in a present frame as an object to be processed for reducing noise presently and another level control value that has been used in another frame preceding to the present frame by one frame temporally;

a storage unit storing the level control value after the smoothing process;

a spectral adjustment unit multiplying the level control value after the smoothing process, of the frame as the object to be processed for reducing noise, by the frequency signals of the frame thereby executing a level adjustment; and

a reverse frequency converter converting the frequency signals, whose levels have been controlled by the spectral adjustment unit, into a time-domain audio signals.

2. The audio signal processing device of claim 1, further comprising a controller that controls the level control value setting unit so as to execute either the reduction amount setting process or the selectively.

3. The audio signal processing device of claim 1, wherein

the first to fourth threshold values are values established with respect to each spectrum in the frame or each frequency band therein.

4. The audio signal processing device of claim 1, wherein

the level control value setting unit sets the level control value so that the frequency characteristic of an amplification amount based on the level control value established at the amplification amount setting process changes corresponding to a genre of contents including the audio signals.

5. The audio signal processing device of claim 1, wherein

the level control value smoothing unit determines a time constant of smoothing for the level control value established in the amplification amount setting process with use of:

an allowable noise level value based on a frequency characteristic of human auditory sense in response to a predetermined sound volume;

the third threshold value; and

the level control value that the level control value setting unit has established in the amplification amount setting process, against a frame to be processed by the noise reduction process.

6. An audio signal processing method comprising the steps of:

dividing inputted audio signals into frames as predetermined units by a frame division unit;

converting the audio signals on a frame-to-frame basis from time-domain signals to frequency signals as frequency-domain signals by a frequency converter;

detecting respective levels of spectrums of respective frequencies from the frequency signals with respect to each frame by a level detector;

executing a reduction amount setting process of setting a level control value for reducing the levels of the spectrums having levels within a level range between a first threshold value and a second threshold value set lower than the first threshold value, with respect to each frame by a level control value setting unit;

executing an amplification amount setting process of setting a level control value for increasing the level of a spectrum in a predetermined frequency band having a level within a range between a third threshold value set more than the first threshold value and a fourth threshold value set more than the first threshold value and less than the third threshold value, with respect to each frame;

executing a smoothing process of temporally smoothing a difference between one level control value set in a present frame as an object to be processed for reducing noise presently and another level control value that has been used in another frame preceding to the present frame by one frame temporally by a level control value smoothing unit;

storing the level control value after the smoothing process in a storage unit;

multiplying the level control value after the smoothing process, of the frame as the object to be processed for reducing noise, by the frequency signals of the frame thereby executing a level control by a spectral adjustment unit; and

converting the frequency signals, whose levels have been controlled by the spectral adjustment unit, into time-domain audio signals by a reverse frequency converter.