Classification of audio signals

• US 8,438,019 B2
• Filed: 02/22/2005
• Issued: 05/07/2013
• Est. Priority Date: 02/23/2004
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Vainio, Janne, Mikkola, Hannu, Ojala, Pasi, Mkinen, Jari
• Primary Examiner(s): Armstrong, Angela A
• Application Number:
  US11/063,664
• Publication Number:
  US 20050192798A1
• Time in Patent Office: 2,996 Days
• Field of Search: 704219-223, 704/201
• 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 apparatus comprising:

a processor;

a memory including machine executable instructions, the memory and the machine executable instructions being configured to, in association with the processor, cause the apparatus to;

receive frames of an audio signal in a frequency band;

perform a first excitation for a speech like audio signal which is mostly speech signal; and

perform a second excitation for a music like audio signal;

wherein the apparatus is further caused to;

divide the frequency band into at least a first and a second group of sub band audio signals, wherein each sub band audio signal has a narrower bandwidth than said frequency band, and said second group containing sub bands of higher frequencies than said first group;

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

select one excitation among said at least first excitation and said second excitation, the selection based on a defined 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; and

perform the selected excitation for a frame of the audio signal.

2. The apparatus according to claim 1, wherein the apparatus is configured to leave one or more sub bands of the available sub bands outside of said first and said second group of sub bands.

3. The apparatus according to claim 2, wherein the apparatus is configured to leave the sub band of lowest frequencies outside of said first and said second group of sub bands.

4. The apparatus according to claim 1, wherein said apparatus is embodied as an adaptive multi-rate wideband codec.

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

6. The apparatus according to claim 1, wherein the apparatus is configured to define a first number of frames and a second number of frames, said second number being greater than said first number, wherein said apparatus is configured to calculate a first average standard deviation value using the normalised signal energies of the first number of frames including the current frame at each sub band and to calculate a second average standard deviation value using the normalised signal energies of the second number of frames including the current frame at each sub band.

7. The apparatus according to claim 1, wherein said apparatus is at least partially embodied as a filter bank of a voice activity detector.

8. A device comprising an encoder comprising an input configured to input frames of an audio signal in a frequency band, a first excitation block configured to perform a first excitation for a speech like audio signal which is mostly speech signal, and a second excitation block configured to perform a second excitation for a music like audio signal, wherein said encoder further comprises a filter configured to divide the frequency band into at least a first and a second group of sub band audio signals, wherein each sub band audio signal has a narrower bandwidth than said frequency band and said second group containing sub bands of higher frequencies than said first group wherein said filter further comprises a filter block configured to produce information indicative of normalised signal energies of a current frame of the audio signal at least at one sub band;

and the device also comprising an excitation selection block configured to select one excitation block among said at least first excitation block and said second excitation block, the selection based on a defined 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 so that the selected excitation block performs the excitation for a frame of the audio signal.

9. The device according to claim 8, wherein the device is configured to leave one or more sub bands of the available sub bands outside of said first and said second group of sub bands.

10. The device according to claim 9, wherein the device is configured to leave the sub band of lowest frequencies outside of said first and said second group of sub bands.

11. The device according to claim 8, wherein the device is configured 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 is configured to calculate a first average standard deviation value using the normalised signal energies of the first number of frames including the current frame at each sub band and to calculate a second average standard deviation value using the normalised signal energies of the second number of frames including the current frame at each sub band.

12. The device according to claim 8, wherein said filter is a filter bank of a voice activity detector.

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

14. The device according to claim 8, wherein said first excitation is Algebraic Code Excited Linear Prediction excitation and said second excitation is transform coded excitation.

15. The device according to claim 8, comprising a transmitter configured to transmit frames including parameters produced by the selected excitation block through a low bit rate channel.

16. A mobile communication device comprising an encoder comprising an input configured to input frames of an audio signal in a frequency band, a first excitation block configured to perform a first excitation for a speech like audio signal which is mostly speech signal, and a second excitation block configured to perform a second excitation for a music like audio signal, wherein said encoder further comprises a filter configured to divide the frequency band into at least a first and a second group of sub band audio signals, wherein each sub band audio signal has a narrower bandwidth than said frequency band and said second group containing sub bands of higher frequencies than said first group wherein said filter further comprises a filter block configured to produce information indicative of normalised signal energies of a current frame of the audio signal at least at one sub band;

and the device also comprising an excitation selection block configured to select one excitation block among said at least first excitation block and a second excitation block, the selection based on a defined 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 so that the selected excitation block performs the excitation for a frame of the audio signal.

17. A system comprising an encoder comprising:

a processor;

a memory including machine executable instructions, the memory and the machine executable instructions being configured to, in association with the processor, cause the encoder to;

receive frames of an audio signal in a frequency band;

perform a first excitation for a speech like audio signal which is mostly speech signal; and

perform a second excitation for a music like audio signal;

wherein said encoder is further caused to;

divide the frequency band into at least a first and a second group of sub band audio signals, wherein each sub band audio signal has a narrower bandwidth than said frequency band and said second group containing sub bands of higher frequencies than said first group;

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

select one excitation among said at least first excitation and said second excitation, the selection based on a defined 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; and

perform the selected excitation for a frame of the audio signal.

18. The system according to claim 17, wherein the encoder is configured to leave one or more sub bands of the available sub bands outside of said first and said second group of sub bands.

19. The system according to claim 18, wherein the encoder is configured to leave the sub band of lowest frequencies outside of said first and said second group of sub bands.

20. The system according to claim 17, wherein the system is configured to define a first number of frames and a second number of frames, said second number being greater than said first number, wherein said encoder is configured to calculate a first average standard deviation value using normalised signal energies of the first number of frames including the current frame at each sub band and to calculate a second average standard deviation value using normalised signal energies of the second number of frames including the current frame at each sub band.

21. The system according to claim 17, wherein said encoder is at least partially embodied as a filter bank of a voice activity detector.

22. The system according to claim 17, wherein said encoder is embodied as an adaptive multi-rate wideband codec.

23. The system according to claim 17, wherein said first excitation is Algebraic Code Excited Linear Prediction excitation and said second excitation is transform coded excitation.

24. The system according to claim 17, wherein the encoder is an encoder of a mobile communication device.

25. The system according to claim 17, further comprising a transmitter configured to transmit frames including parameters produced by the selected excitation through a low bit rate channel.

26. A method comprising:

receiving input frames of an audio signal in a frequency band at a device;

using a first excitation for a speech like audio signal which is mostly speech signal;

using a second excitation for a music like audio signal;

dividing the frequency band into at least a first and a second group of sub band audio signals, wherein each sub band audio signal has a narrower bandwidth than said frequency band and said second group containing sub bands of higher frequencies than said first group;

producing information indicative of normalised signal energies of a current frame of the audio signal at least at one sub band by using a filter block;

selecting one excitation among said at least first excitation and said second excitation by defining 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 using said relation in the selection of the excitation; and

using the selected excitation to perform the excitation for a frame of the audio signal.

27. The method according to claim 26 comprising:

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

28. The method according to claim 27 comprising:

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

29. The method according to claim 26 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 normalised 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 normalised signal energies of the second number of frames including the current frame at each sub band.

30. The method according to claim 26 comprising transmitting frames including parameters produced by the selected excitation through a low bit rate channel.

31. A non-transitory computer readable medium stored with instructions, which when executed by a processor, perform:

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

dividing the frequency band into at least a first and a second group of sub band audio signals, wherein each sub band audio signal has a narrower bandwidth than said frequency band and said second group containing sub bands of higher frequencies than said first group;

producing information indicative of normalised signal energies of a current frame of the audio signal at least at one sub band by using a filter block;

selecting one excitation among said at least first excitation and said second excitation by defining 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 using said relation in the selection of the excitation; and

using the selected excitation to perform the excitation for a frame of the audio signal.

32. The computer readable medium according to claim 31, 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 readable medium is further stored with instructions, which when executed by a processor, perform:

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

33. The computer readable medium according to claim 31 further stored with instructions, which when executed by a processor, perform:

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

transform coded excitation as said second excitation.