Method and apparatus for extracting pitch information from audio signal using morphology

• US 20070106503A1
• Filed: 07/11/2006
• Published: 05/10/2007
• Est. Priority Date: 07/11/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Hyun-Soo
• Granted Patent: US 7,822,600 B2
• Time in Patent Office: Days
• US Class Current: 704/211
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals

Abstract

A function of improving accuracy of the extraction of pitch information in an audio signal including voice and sound signals is implemented. To do this, a morphological operation is used. In detail, an input audio signal is converted to an audio signal in a frequency domain, an optimum structuring set size (SSS) is determined, and a morphological operation is performed using the determined SSS. Then, by extracting the highest peak from a signal obtained through a predetermined fold and summation process as pitch information, the pitch information can be used in all audio systems in the latter part when voice coding, recognition, synthesis, and/or robustness are performed.

Claims

1. A method of extracting pitch information from an audio signal using morphology, the method comprising the steps of:

when the audio signal is input, converting it to a frequency domain;

determining an optimum structuring set size (SSS) of a morphological filter performing a morphological closing of a waveform of the converted audio signal;

performing a morphological operation using the determined SSS;

extracting harmonic peaks as the result of the morphological operation; and

extracting pitch information using the extracted harmonic peaks.

2. The method of claim 1, wherein, in the step of converting to the frequency domain, the audio signal in a time domain is converted to an audio signal in the frequency domain.

3. The method of claim 1, further comprising the steps of:

performing the morphological closing of the waveform of the converted audio signal; and

preprocessing the morphological closed signal.

4. The method of claim 3, wherein, in the step of preprocessing, only a harmonic signal remains by removing a staircase signal from the waveform of the converted audio signal.

5. The method of claim 1, wherein, in the step of extracting the pitch information, the highest peak obtained by performing a predetermined fold and summation process for the extracted harmonic peaks is deemed as the pitch information.

6. The method of claim 1, wherein the step of determining the optimum SSS comprises the steps of:

setting the number of maximum harmonic peaks after preprocessing the waveform of the converted audio signal;

calculating an energy ratio according to the set number of maximum harmonic peaks;

comparing the energy ratio to a current SSS; and

determining the optimum SSS by adjusting the number of maximum harmonic peaks according to the comparison result.

7. The method of claim 6, wherein, in the step of calculating the energy ratio, after defining the number of maximum harmonic peaks as N, obtaining P, which is a ratio of the energy of the N selected harmonic peaks to the energy of the total remainder peaks, using the N selected harmonic peaks.

8. The method of claim 7, wherein the optimum SSS is obtained by decreasing N if the energy ratio P exceeds a predetermined value, and by increasing N if the energy ratio P less than the predetermined value.

9. An apparatus for extracting pitch information from an audio signal using morphology, the apparatus comprising:

an audio signal input unit for receiving the audio signal;

a frequency domain converter for converting the input audio signal in a time domain to an audio signal in a frequency domain;

a structuring set size (SSS) determiner for determining an optimum SSS of a waveform of the converted audio signal;

a morphological filter for performing a morphological operation using the determined SSS; and

a harmonic peak extractor for extracting harmonic peaks as the result of the morphological operation and extracting pitch information using the extracted harmonic peaks.

10. The apparatus of claim 9, wherein the morphological filter performs preprocessing after performing morphological closing of the waveform of the converted audio signal.

11. The apparatus of claim 10, wherein, in the preprocessing, only a harmonic signal remains by removing a staircase signal from the waveform of the converted audio signal.

12. The apparatus of claim 9, wherein the harmonic peak extractor determines the highest peak obtained by performing a predetermined fold and summation process for the extracted harmonic peaks which is deemed to be the pitch information.

13. The apparatus of claim 9, wherein the SSS determiner determines the optimum SSS by setting the number of maximum harmonic peaks after preprocessing the waveform of the converted audio signal, calculating an energy ratio according to the set number of maximum harmonic peaks, comparing the energy ratio to a current SSS, and adjusting the number of maximum harmonic peaks according to the comparison result.