Classification of audio signals

• US 20050192798A1
• Filed: 02/22/2005
• Published: 09/01/2005
• Est. Priority Date: 02/23/2004
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Ojala, Pasi, Makinen, Jari, Vainio, Janne, Mikkola, Hannu
• Granted Patent: US 8,438,019 B2
• Time in Patent Office: Days
• US Class Current: 704/223
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding

Abstract

An encoder comprising an input for inputting frames of an audio signal in a frequency band, at least a first excitation block for performing a first excitation for a speech like audio signal, and a second excitation block for performing a second excitation for a non-speech like audio signal. The encoder further comprises a filter for dividing the frequency band into a plurality of sub bands each having a narrower bandwidth than the frequency band. The encoder also comprises an excitation selection block for selecting one excitation block among the at least first excitation block and the second excitation block for performing the excitation for a frame of the audio signal on the basis of the properties of the audio signal at least at one of the sub bands. The invention also relates to a device, a system, a method and a storage medium for a computer program.

Claims

1. An encoder comprising an input for inputting frames of an audio signal in a frequency band, at least a first excitation block for performing a first excitation for a speech like audio signal, and a second excitation block for performing a second excitation for a non-speech like audio signal, wherein the encoder further comprises a filter for dividing the frequency band into a plurality of sub bands each having a narrower bandwidth than said frequency band, and an excitation selection block for selecting one excitation block among said at least first excitation block and said second excitation block for performing the excitation for a frame of the audio signal on the basis of the properties of the audio signal at least in one of said sub bands.

2. The encoder according to claim 1, wherein said filter comprises a filter block for producing information indicative of signal energies of a current frame of the audio signal at least at one sub band, and said excitation selection block comprises energy determining means for determining the signal energy information of at least one sub band.

3. The encoder according to claim 2, wherein the encoder is adapted to define at least a first and a second group of sub bands, said second group containing sub bands of higher frequencies than said first group, and the encoder is further adapted to define a relation between normalised signal energy of said first group of sub bands and normalised signal energy of said second group of sub bands for the frames of the audio signal, and to use said relation in the selection of the excitation block.

4. The encoder according to claim 3, wherein the encoder is adapted to leave one or more sub bands of the available sub bands outside of said first and said second group of sub bands.

5. The encoder according to claim 4, wherein the encoder is adapted to leave the sub band of lowest frequencies outside of said first and said second group of sub bands.

6. The encoder according to claim 3, wherein the encoder is adapted to define a first number of frames and a second number of frames, said second number being greater than said first number, wherein said excitation selection block comprises calculation means for calculating a first average standard deviation value using signal energies of the first number of frames including the current frame at each sub band and for calculating a second average standard deviation value using signal energies of the second number of frames including the current frame at each sub band.

7. The encoder according to claim 1, wherein said filter is a filter bank of a voice activity detector.

8. The encoder according to claim 1, wherein said encoder is an adaptive multi-rate wideband codec.

9. The encoder according to claim 1, wherein said first excitation is Algebraic Code Excited Linear Prediction excitation and said second excitation is transform coded excitation.

10. A device comprising an encoder comprising an input for inputting frames of an audio signal in a frequency band, at least a first excitation block for performing a first excitation for a speech like audio signal, and a second excitation block for performing a second excitation for a non-speech like audio signal, wherein said encoder further comprises a filter for dividing the frequency band into a plurality of sub bands each having a narrower bandwidth than said frequency band, the device also comprising an excitation selection block for selecting one excitation block among said at least first excitation block and said second excitation block for performing the excitation for a frame of the audio signal on the basis of the properties of the audio signal at least at one of said sub bands.

11. The device according to claim 10, wherein said filter comprises a filter block for producing information indicative of signal energies (E(n)) of a current frame of the audio signal at least at one sub band, and said excitation selection block comprises energy determining means for determining the signal energy information of at least one sub band.

12. The device according to claim 11, wherein the device is adapted to define at least a first and a second group of sub bands, said second group containing sub bands of higher frequencies than said first group, and the device is further adapted to define a relation between normalised signal energy of said first group of sub bands and normalised signal energy of said second group of sub bands for the frames of the audio signal, and to use said relation in the selection of the excitation block.

13. The device according to claim 12, wherein the device is adapted to leave one or more sub bands of the available sub bands outside of said first and said second group of sub bands.

14. The device according to claim 13, wherein the device is adapted to leave the sub band of lowest frequencies outside of said first and said second group of sub bands.

15. The device according to claim 12, wherein the device is adapted to define a first number of frames and a second number of frames, said second number being greater than said first number, wherein said excitation selection block comprises calculation means for calculating a first average standard deviation value using signal energies of the first number of frames including the current frame at each sub band and for calculating a second average standard deviation value using signal energies of the second number of frames including the current frame at each sub band.

16. The device according to claim 10, wherein said filter is a filter bank of a voice activity detector.

17. The device according to claim 10, wherein said encoder is an adaptive multi-rate wideband codec.

18. The device according to claim 10, wherein said first excitation is Algebraic Code Excited Linear Prediction excitation and said second excitation is transform coded excitation.

19. The device according to claim 10, comprising a transmitter for transmitting frames including parameters produced by the selected excitation block through a low bit rate channel.

20. A mobile communication device comprising an encoder comprising an input for inputting frames of an audio signal in a frequency band, at least a first excitation block for performing a first excitation for a speech like audio signal, and a second excitation block for performing a second excitation for a non-speech like audio signal, wherein said encoder further comprises a filter for dividing the frequency band into a plurality of sub bands each having a narrower bandwidth than said frequency band, the device also comprising an excitation selection block for selecting one excitation block among said at least first excitation block and said second excitation block for performing the excitation for a frame of the audio signal on the basis of the properties of the audio signal at least at one of said sub bands.

21. A system comprising an encoder comprising an input for inputting frames of an audio signal in a frequency band at least a first excitation block for performing a first excitation for a speech like audio signal, and a second excitation block for performing a second excitation for a non-speech like audio signal, wherein said encoder further comprises a filter for dividing the frequency band into a plurality of sub bands each having a narrower bandwidth than said frequency band, that the system also comprises an excitation selection block for selecting one excitation block among said at least first excitation block and said second excitation block for performing the excitation for a frame of the audio signal on the basis of the properties of the audio signal at least at one of said sub bands.

22. The system according to claim 21, wherein said filter comprises a filter block for producing information indicative of signal energies (E(n)) of a current frame of the audio signal at least at one sub band, and that said excitation selection block comprises energy determining means for determining the signal energy information of at least one sub band.

23. The system according to claim 22, wherein the system is adapted to define at least a first and a second group of sub bands, said second group containing sub bands of higher frequencies than said first group, and the system is further adapted to define a relation (LPH) between normalised signal energy (LevL) of said first group of sub bands and normalised signal energy (LevH) of said second group of sub bands for the frames of the audio signal, and that said relation (LPH) is arranged to be used in the selection of the excitation block.

24. The system according to claim 23, wherein the encoder is adapted to leave one or more sub bands of the available sub bands outside of said first and said second group of sub bands.

25. The system according to claim 24, wherein the encoder is adapted to leave the sub band of lowest frequencies outside of said first and said second group of sub bands.

26. The system according to claim 23, wherein the system is adapted to define a first number of frames and a second number of frames, said second number being greater than said first number, wherein said excitation selection block comprises calculation means for calculating a first average standard deviation value using signal energies of the first number of frames including the current frame at each sub band and for calculating a second average standard deviation value using signal energies of the second number of frames including the current frame at each sub band.

27. The system according to claim 21, wherein said filter is a filter bank of a voice activity detector.

28. The system according to claim 21, wherein said encoder is an adaptive multi-rate wideband codec.

29. The system according to claim 21, wherein said first excitation is Algebraic Code Excited Linear Prediction excitation and said second excitation is transform coded excitation.

30. The system according to claim 21, wherein the encoder is an encoder of a mobile communication device.

31. The system according to claim 21, wherein it comprises a transmitter for transmitting frames including parameters produced by the selected excitation block through a low bit rate channel.

32. A method for compressing audio signals in a frequency band comprising:

using a first excitation for a speech like audio signal;

using a second excitation for a non-speech like audio signal;

dividing the frequency band into a plurality of sub bands each having a narrower bandwidth than said frequency band,

selecting one excitation among said at least first excitation and said second excitation for performing the excitation for a frame of the audio signal on the basis of the properties of the audio signal at least at one of said sub bands.

33. The method according to claim 32, further comprising:

producing by said filter information indicative of signal energies of a current frame of the audio signal at least one sub band; and

determining signal energy information of at least one sub band by said excitation selection block.

34. The method according to claim 33 comprising:

defining at least a first and a second group of sub bands, said second group containing sub bands of higher frequencies than said first group;

defining a relation (LPH) between normalised signal energy (LevL) of said first group of sub bands and normalised signal energy (LevH) of said second group of sub bands for the frames of the audio signal; and

using said relation in the selection of the excitation block.

35. The method according to claim 34 comprising:

leaving one or more sub bands of the available sub bands outside of said first and said second group of sub bands.

36. The method according to claim 35 comprising:

leaving the sub band of lowest frequencies outside of said first and said second group of sub bands.

37. The method according to claim 34 comprising:

defining a first number of frames and a second number of frames, said second number being greater than said first number;

calculating a first average standard deviation value using signal energies of the first number of frames including the current frame at each sub band; and

calculating a second average standard deviation value using signal energies of the second number of frames including the current frame at each sub band.

38. The method according to claim 32 comprising transmitting frames including parameters produced by the selected excitation through a low bit rate channel.

39. A module for classifying frames of an audio signal in a frequency band for selection of an excitation among at least a first excitation for a speech like audio signal, and a second excitation for a non-speech like audio signal, wherein the module further comprises input for inputting information indicative of the frequency band divided into a plurality of sub bands each having a narrower bandwidth than said frequency band, and an excitation selection block for selecting one excitation block among said at least first excitation block and said second excitation block for performing the excitation for a frame of the audio signal on the basis of the properties of the audio signal at least at one of said sub bands.

40. The module according to claim 39, wherein the module is adapted to define at least a first and a second group of sub bands, said second group containing sub bands of higher frequencies than said first group;

and the module is further adapted to define a relation between normalised signal energy of said first group of sub bands and normalised signal energy of said second group of sub bands for the frames of the audio signal, and to use said relation in the selection of the excitation block.

41. The module according to claim 40, wherein the module is adapted to leave one or more sub bands of the available sub bands outside of said first and said second group of sub bands.

42. The module according to claim 41, wherein the module is adapted to leave the sub band of lowest frequencies outside of said first and said second group of sub bands.

43. The module according to claim 40, wherein the module is adapted to define a first number of frames and a second number of frames, said second number being greater than said first number;

wherein said excitation selection block comprises calculation means for calculating a first average standard deviation value using signal energies of the first number of frames including the current frame at each sub band and for calculating a second average standard deviation value using signal energies of the second number of frames including the current frame at each sub band.

44. A computer program product comprising machine executable steps stored on a readable medium for execution by a processor, said machine executable steps when executed for:

compressing audio signals in a frequency band, in which a first excitation is used for a speech like audio signal, and second excitation is used for a non-speech like audio signal;

dividing the frequency band into a plurality of sub bands each having a narrower bandwidth than said frequency band; and

selecting one excitation among said at least first excitation and said second excitation on the basis of the properties of the audio signal at least at one of said sub bands for performing the excitation for a frame of the audio signal.

45. The computer program product according to claim 44 further comprising machine executable steps for

producing information indicative of signal energies of a current frame of the audio signal at least one sub band;

and

determining the signal energy information of at least one sub band.

46. The computer program product according to claim 45, wherein a first number of frames and a second number of frames are defined, said second number being greater than said first number, wherein the computer program product further comprises machine executable steps for

calculating a first average standard deviation value using signal energies of the first number of frames including the current frame at each sub band;

and

calculating a second average standard deviation value using signal energies of the second number of frames including the current frame at each sub band.

47. The computer program product according to claim 44 further comprising machine executable steps for

performing Algebraic Code Excited Linear Prediction excitation as said first excitation;

and

performing transform coded excitation as said second excitation.