Detection of clipping event in audio signals

• US 10,346,125 B2
• Filed: 08/18/2015
• Issued: 07/09/2019
• Est. Priority Date: 08/18/2015
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Fukuda, Takashi, Ichikawa, Osamu
• Primary Examiner(s): Maung, Thomas H
• Application Number:
  US14/829,482
• Publication Number:
  US 20170052758A1
• Time in Patent Office: 1,421 Days
• CPC Class Codes: G06F 3/165 Management of the audio stream, e.g. setting of volume, audio stream path
• CPC Class Codes: G10L 15/02 Feature extraction for speech recognition; Selection of recognition unit
• 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: G10L 21/0232 Processing in the frequency domain
• CPC Class Codes: H03G 11/00 Limiting amplitude; Limiting rate of change of amplitude ; Clipping in general
• CPC Class Codes: H03G 3/002 Control of digital or coded signals H03G3/3089 take precedence

Abstract

A method, a system, and a computer program product detect a clipping event in audio signals. The method includes digitalizing audio signals having limited frequency bands, at a sampling frequency which is greater than two times as large as the maximum frequency component of the audio signal; and detecting a clipping event of the audio signals, based on magnitudes of spectrum in a bandwidth which is greater than or equal to the limited frequency band. The sampling frequency may be greater than or equal to three times as large as the maximum frequency component of the audio signal. The detection of a clipping event may include determining, for each frame, whether or not a sum or average of the magnitudes of spectrum at the bandwidth which is greater than or equal to the limited frequency band is larger than a predetermined threshold.

Claims

1. A computer-implemented method for detecting a clipping event in audio signals, the method comprising:

digitalizing audio signals having limited frequency bands, at a sampling frequency which is greater than two times as large as the maximum frequency component of the audio signal;

detecting a clipping event of the audio signals, based on magnitudes of spectrum in a bandwidth which is greater than or equal to the limited frequency band;

dividing the digitalized audio signals into plural frames; and

obtaining, for each frame, spectra by a frequency analysis,

wherein the detection of a clipping event comprises detecting, for each frame, a clipping event of the audio signals, and a clipping event data set is constructed by combining one or more detected clipping events, a level of the clipping events varying over time responsive to a power level of the audio signal input, and

wherein clipping occurs at a level between the maximum frequency component and half of the sampling frequency.

2. The method according to claim 1, wherein the sampling frequency is greater than or equal to three times as large as the maximum frequency component of the audio signal.

3. The method according to claim 1, wherein the sampling frequency is greater than or equal to four times as large as the maximum frequency component of the audio signal.

4. The method according to claim 1, wherein the detection of a clipping event comprises determining whether or not a sum or average of the magnitudes of spectrum at the bandwidth which is greater than or equal to the limited frequency band is larger than a predetermined threshold.

5. The method according to claim 1, wherein the detection of a clipping event comprises determining, for each frame, whether or not a sum or average of the magnitudes of spectrum at the bandwidth which is greater than or equal to the limited frequency band is larger than a predetermined threshold.

6. The method according to claim 5, wherein the detection of a clipping event comprises determining that the frame which is a subject of the determination comprises a clipping event, if the determination is positive.

7. The method according to claim 1, further comprising computing a frequency bin with reference to a sampling period of a data converter as follows:

Bin=f_SAMPLE/N_RECORD=1/(N_RECORD×

M_SAMPLE),

where f_SAMPLE denotes the sampling frequency;

N_RECORD denotes a number of signal points captured in a time domain;

Δ

t_SAMPLE denotes a time interval in each of a plurality of signal points;

N_RECORD/2 denotes a number of frequency points or lines or bands in the spectrum;

a first frequency line in the spectrum represents DC (frequency=0);

a last frequency line can be found at f_SAMPLE/2−

f_SAMPLE/N_RECORD; and

frequency lines are spaced at even intervals of f_SAMPLE/N_RECORD.

8. A system, comprising:

a processor; and

a memory storing a program, which, when executed on the processor, performs an operation for detecting a clipping event in audio signals, the operation comprising;

digitalizing audio signals having limited frequency bands, at a sampling frequency which is greater than two times as large as the maximum frequency component of the audio signal;

detecting a clipping event of the audio signals, based on magnitudes of spectrum in a bandwidth which is greater than or equal to the limited frequency band;

dividing the digitalized audio signals into plural frames; and

obtaining, for each frame, spectra by a Fast Fourier Transform,

wherein the detection of a clipping event comprises detecting, for each frame, a clipping event of the audio signals, and a clipping event data set is constructed by combining one or more detected clipping events, a level of the clipping events varying over time responsive to a power level of the audio signal input, and

wherein clipping occurs at a level between the maximum frequency component and half of the sampling frequency.

9. The system according to claim 8, wherein the sampling frequency is greater than or equal to three times as large as the maximum frequency component of the audio signal.

10. The system according to claim 8, wherein the detection of a clipping event comprises determining whether or not a sum or average of the magnitudes of spectrum at the bandwidth which is greater than or equal to the limited frequency band is larger than a predetermined threshold.

11. The system according to claim 8, wherein the detection of a clipping event comprises determining, for each frame, whether or not a sum or average of the magnitudes of spectrum at the bandwidth which is greater than or equal to the limited frequency band is larger than a predetermined threshold.

12. The system according to claim 11, wherein the detection of a clipping event comprises determining that the frame which is a subject of the determination comprises a clipping event, if the determination is positive.

13. The system according to claim 8, wherein the system is a speech recognition system.

14. A computer program product for detecting a clipping event in audio signals, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, wherein the computer readable storage medium is not a transitory signal per se, the program instructions executable by a computer to cause the computer to perform a method comprising:

digitalizing audio signals having limited frequency bands, at a sampling frequency which is greater than two times as large as the maximum frequency component of the audio signal;

detecting a clipping event of the audio signals, based on magnitudes of spectrum in a bandwidth which is greater than or equal to the limited frequency band;

dividing the digitalized audio signals into plural frames; and

obtaining, for each frame, spectra by a Fast Fourier Transform,

wherein the detection of a clipping event comprises detecting, for each frame, a clipping event of the audio signals, and a clipping event data set is constructed by combining one or more detected clipping events, a level of the clipping events varying over time responsive to a power level of the audio signal input, and

wherein clipping occurs at a level between the maximum frequency component and half of the sampling frequency.

15. The computer program product according to claim 14, wherein the sampling frequency is greater than or equal to three times as large as the maximum frequency component of the audio signal.

16. The computer program product according to claim 14, wherein the detection of a clipping event comprises determining whether or not a sum or average of the magnitudes of spectrum at the bandwidth which is greater than or equal to the limited frequency band is larger than a predetermined threshold.

17. The computer program product according to claim 15, wherein the detection of a clipping event comprises determining, for each frame, whether or not a sum or average of the magnitudes of spectrum at the bandwidth which is greater than or equal to the limited frequency band is larger than a predetermined threshold.

18. The computer program product according to claim 17, wherein the detection of a clipping event comprises determining that the frame which is a subject of the determination comprises a clipping event, if the determination is positive.