METHOD AND APPARATUS FOR ENCODING AND DECODING AUDIO SIGNALS

• US 20090187409A1
• Filed: 10/08/2007
• Published: 07/23/2009
• Est. Priority Date: 10/10/2006
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Krishnan, Venkatesh, Rajendran, Vivek, Kandhadai, Ananthapadmanabhan A.
• Granted Patent: US 9,583,117 B2
• Time in Patent Office: Days
• US Class Current: 704/262
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding
• CPC Class Codes: G10L 19/22 Mode decision, i.e. based on audio signal content versus external parameters

Abstract

Techniques for efficiently encoding an input signal are described. In one design, a generalized encoder encodes the input signal (e.g., an audio signal) based on at least one detector and multiple encoders. The at least one detector may include a signal activity detector, a noise-like signal detector, a sparseness detector, some other detector, or a combination thereof. The multiple encoders may include a silence encoder, a noise-like signal encoder, a time-domain encoder, a transform-domain encoder, some other encoder, or a combination thereof. The characteristics of the input signal may be determined based on the at least one detector. An encoder may be selected from among the multiple encoders based on the characteristics of the input signal. The input signal may be encoded based on the selected encoder. The input signal may include a sequence of frames, and detection and encoding may be performed for each frame.

Claims

1. An apparatus comprising:

at least one processor configured to determine characteristics of an input signal based on at least one detector comprising a noise-like signal detector, to select an encoder from among multiple encoders based on the determined characteristics of the input signal, the multiple encoders comprising a time-domain encoder and at least one transform-domain encoder for encoding signals having sparse transform-domain representations in transform domain, and to encode the input signal based on the selected encoder; and

a memory coupled to the at least one processor.

2. The apparatus of claim 1, wherein the input signal is an audio signal.

3. The apparatus of claim 1, wherein the multiple encoders comprise a silence encoder, and wherein the at least one processor is configured to detect for activity in the input signal and to select the silence encoder if activity is not detected in the input signal.

4. The apparatus of claim 1, wherein the multiple encoders comprise a noise-like signal encoder, and wherein the at least one processor is configured to determine whether the input signal has noise-like signal characteristics and to select the noise-like signal encoder if the input signal has noise-like signal characteristics.

5. The apparatus of claim 4, wherein the noise-like signal encoder comprises a Noise Excited Linear Prediction (NELP) encoder.

6. The apparatus of claim 1, wherein the at least one processor is configured to determine sparseness of the input signal in time domain, to determine sparseness of the input signal in at least one transform domain for the at least one transform-domain encoder, to select the time-domain encoder if the input signal is determined to be more sparse in the time domain than the at least one transform domain, and to select one of the at least one transform-domain encoder if the input signal is determined to be more sparse in a corresponding transform domain than the time domain and other transform domains, if any.

7. The apparatus of claim 6, wherein the time-domain encoder comprises a Code Excited Linear Prediction (CELP) encoder and the at least one transform-domain encoder comprises a Modified Discrete Cosine Transform (MDCT) encoder.

8. The apparatus of claim 1, wherein the input signal comprises a sequence of frames, and wherein the at least one processor is configured to determine the characteristics of each frame in the sequence, to select an encoder for each frame based on the determined characteristics of the frame, and to encode each frame based on the encoder selected for the frame.

9. The apparatus of claim 8, wherein the at least one processor is configured to select a particular encoder for a particular frame if the particular frame and a predetermined number of preceding frames indicate a switch to the particular encoder.

10. The apparatus of claim 1, wherein the apparatus is a mobile phone.

11. The apparatus of claim 1, wherein the apparatus is a mobile phone comprising a Code Division Multiple Access (CDMA) transceiver.

12. A method comprising:

determining characteristics of an input signal based on at least one detector comprising a noise-like signal detector;

selecting an encoder from among multiple encoders based on the determined characteristics of the input signal, the multiple encoders comprising a time-domain encoder and at least one transform-domain encoder for encoding signals having sparse transform-domain representations in transform domain; and

encoding the input signal based on the selected encoder.

13. The method of claim 12, wherein the multiple encoders comprise a silence encoder, wherein the determining the characteristics of the input signal comprises detecting for activity in the input signal, and wherein the selecting the encoder based on the determined characteristics of the input signal comprises selecting the silence encoder if activity is not detected in the input signal.

14. The method of claim 12, wherein the multiple encoders comprise a noise-like signal encoder, wherein the determining the characteristics of the input signal comprises determining whether the input signal has noise-like signal characteristics, and wherein the selecting the encoder based on the determined characteristics of the input signal comprises selecting the noise-like signal encoder if the input signal has noise-like signal characteristics.

15. The method of claim 12, wherein the determining the characteristics of the input signal comprises determining sparseness of the input signal in time domain and at least one transform domain for the at least one transform-domain encoder, and wherein the selecting the encoder based on the determined characteristics of the input signal comprises

selecting the time-domain encoder if the input signal is determined to be more sparse in the time domain than the at least one transform domain, and

selecting one of the at least one transform-domain encoder if the input signal is determined to be more sparse in a corresponding transform domain than the time domain and other transform domains, if any.

16. An apparatus comprising:

means for determining characteristics of an input signal based on at least one detector comprising a noise-like signal detector;

means for selecting an encoder from among multiple encoders based on the determined characteristics of the input signal, the multiple encoders comprising a time-domain encoder and at least one transform-domain encoder for encoding signals having sparse transform-domain representations in transform domain; and

means for encoding the input signal based on the selected encoder.

17. The apparatus of claim 16, wherein the multiple encoders comprise a silence encoder, wherein the means for determining the characteristics of the input signal comprises means for detecting for activity in the input signal, and wherein the means for selecting the encoder based on the determined characteristics of the input signal comprises means for selecting the silence encoder if activity is not detected in the input signal.

18. The apparatus of claim 16, wherein the multiple encoders comprise a noise-like signal encoder, wherein the means for determining the characteristics of the input signal comprises means for determining whether the input signal has noise-like signal characteristics, and wherein the means for selecting the encoder based on the determined characteristics of the input signal comprises means for selecting the noise-like signal encoder if the input signal has noise-like signal characteristics.

19. The apparatus of claim 16, wherein the means for determining the characteristics of the input signal comprises means for determining sparseness of the input signal in time domain and at least one transform domain for the at least one transform-domain encoder, and wherein the means for selecting the encoder based on the determined characteristics of the input signal comprises

means for selecting the time-domain encoder if the input signal is determined to be more sparse in the time domain than the at least one transform domain, and

means for selecting one of the at least one transform-domain encoder if the input signal is determined to be more sparse in a corresponding transform domain than the time domain and other transform domains, if any.

20. A processor-readable media for storing instructions to:

determine characteristics of an input signal based on at least one detector comprising a noise-like signal detector;

select an encoder from among multiple encoders based on the determined characteristics of the input signal, the multiple encoders comprising a time-domain encoder and at least one transform-domain encoder for encoding signals having sparse transform-domain representations in transform domain; and

encode the input signal based on the selected encoder.

21. An apparatus comprising:

at least one processor configured to determine sparseness of an input signal in each of multiple domains, to select an encoder from among multiple encoders based on the sparseness of the input signal in the multiple domains, and to encode the input signal based on the selected encoder; and

a memory coupled to the at least one processor.

22. The apparatus of claim 21, wherein the multiple domains comprise time domain and transform domain, and wherein the at least one processor is configured to determine sparseness of the input signal in the time domain and the transform domain, to select a time-domain encoder to encode the input signal in the time domain if the input signal is determined to be more sparse in the time domain than the transform domain, and to select a transform-domain encoder to encode the input signal in the transform domain if the input signal is determined to be more sparse in the transform domain than the time domain.

23. The apparatus of claim 21, wherein the multiple domains comprise time domain and transform domain, and wherein the at least one processor is configured to determine a first parameter indicative of sparseness of the input signal in the time domain, to determine a second parameter indicative of sparseness of the input signal in the transform domain, to select a time-domain encoder if the first and second parameters indicate the input signal being more sparse in the time domain than the transform domain, and to select a transform-domain encoder if the first and second parameters indicate the input signal being more sparse in the transform domain than the time domain.

24. The apparatus of claim 23, wherein the at least one processor is configured to determine at least one count based on prior selections of the time-domain encoder and prior selections of the transform-domain encoder, and to select the time-domain encoder or the transform-domain encoder further based on the at least one count.

25. A method comprising:

determining sparseness of an input signal in each of multiple domains;

selecting an encoder from among multiple encoders based on the sparseness of the input signal in the multiple domains; and

encoding the input signal based on the selected encoder.

26. The method of claim 25, wherein the multiple domains comprise time domain and transform domain, wherein the determining the sparseness of the input signal comprises

determining a first parameter indicative of sparseness of the input signal in the time domain, and

determining a second parameter indicative of sparseness of the input signal in the transform domain, and wherein the selecting an encoder comprises

selecting a time-domain encoder if the first and second parameters indicate the input signal being more sparse in the time domain than the transform domain, and

selecting a transform-domain encoder if the first and second parameters indicate the input signal being more sparse in the transform domain than the time domain.

27. The method of claim 26, further comprising:

determining at least one count based on prior selections of the time-domain encoder and prior selections of the transform-domain encoder, and

wherein the selecting an encoder comprises selecting the time-domain encoder or the transform-domain encoder further based on the at least one count.

28. An apparatus comprising:

at least one processor configured to transform a first signal in a first domain to obtain a second signal in a second domain, to determine first and second parameters based on the first and second signals, and to determine whether the first signal or the second signal is more sparse based on the first and second parameters; and

a memory coupled to the at least one processor.

29. The apparatus of claim 28, wherein the first domain is time domain and the second domain is transform domain.

30. The apparatus of claim 28, wherein the at least one processor is configured to transform the first signal based on a Modified Discrete Cosine Transform (MDCT) to obtain the second signal.

31. The apparatus of claim 28, wherein the at least one processor is configured to determine the first and second parameters. based on energy of values in the first and second signals.

32. The apparatus of claim 28, wherein the at least one processor is configured to perform Linear Predictive Coding (LPC) on an input signal to obtain residuals in the first signal, to transform the residuals in the first signal to obtain coefficients in the second signal, to determine energy values for the residuals in the first signal, to determine energy values for the coefficients in the second signal, and to determine the first and second parameters based on the energy values for the residuals and the energy values for the coefficients.

33. The apparatus of claim 28, wherein the at least one processor is configured to determine the first parameter based on a minimum number of values in the first signal containing at least a particular percentage of total energy of the first signal, and to determine the second parameter based on a minimum number of values in the second signal containing at least the particular percentage of total energy of the second signal.

34. The apparatus of claim 33, wherein the at least one processor is configured to determine that the first signal is more sparse based on the first parameter being smaller than the second parameter by a first threshold, and to determine that the second signal is more sparse based on the second parameter being smaller than the first parameter by a second threshold.

35. The apparatus of claim 33, wherein the at least one processor is configured to determine a third parameter indicative of cumulative energy of the first signal, to determine a fourth parameter indicative of cumulative energy of the second signal, and to determine whether the first signal or the second signal is more sparse further based on the third and fourth parameters.

36. The apparatus of claim 28, wherein the at least one processor is configured to determine a first cumulative energy function for the first signal, to determine a second cumulative energy function for the second signal, to determine the first parameter based on number of times the first cumulative energy function meets or exceeds the second cumulative energy function, and to determine the second parameter based on number of times the second cumulative energy function meets or exceeds the first cumulative energy function.

37. The apparatus of claim 36, wherein the at least one processor is configured to determine that the first signal is more sparse based on the first parameter being greater than the second parameter, and to determine that the second signal is more sparse based on the second parameter being greater than the first parameter.

38. The apparatus of claim 36, wherein the at least one processor is configured to determine a third parameter based on instances in which the first cumulative energy function exceeds the second cumulative energy function, to determine a fourth parameter based on instances in which the second cumulative energy function exceeds the first cumulative energy function, and to determine whether the first signal or the second signal is more sparse further based on the third and fourth parameters.

39. The apparatus of claim 28, wherein the at least one processor is configured to determine at least one count based on prior declarations of the first signal being more sparse and prior declarations of the second signal being more sparse, and to determine whether the first signal or the second signal is more sparse further based on the at least one count.

40. The apparatus of claim 28, wherein the at least one processor is configured to increment a first count and decrement a second count for each declaration of the first signal being more sparse, to decrement the first count and increment the second count for each declaration of the second signal being more sparse, and to determine whether the first signal or the second signal is more sparse based on the first and second counts.

41. A method comprising:

transforming a first signal in a first domain to obtain a second signal in a second domain;

determining first and second parameters based on the first and second signals; and

determining whether the first signal or the second signal is more sparse based on the first and second parameters.

42. The method of claim 41, wherein the determining the first and second parameters comprises

determining the first parameter based on a minimum number of values in the first signal containing at least a particular percentage of total energy of the first signal, and

determining the second parameter based on a minimum number of values in the second signal containing at least the particular percentage of total energy of the second signal.

43. The method of claim 41, further comprising:

determining a first cumulative energy function for the first signal; and

determining a second cumulative energy function for the second signal, and wherein the determining the first and second parameters comprises

determining the first parameter based on number of times the first cumulative energy function meets or exceeds the second cumulative energy function, and

determining the second parameter based on number of times the second cumulative energy function meets or exceeds the first cumulative energy function.

44. The method of claim 43, further comprising:

determining a third parameter based on instances in which the first cumulative energy function exceeds the second cumulative energy function; and

determining a fourth parameter based on instances in which the second cumulative energy function exceeds the first cumulative energy function, and wherein whether the first signal or the second signal is more sparse is determined further based on the third and fourth parameters.

45. The method of claim 41, further comprising:

determining at least one count based on prior declarations of the first signal being more sparse and prior declarations of the second signal being more sparse, and wherein whether the first signal or the second signal is more sparse is determined further based on the at least one count.

46. An apparatus comprising:

at least one processor configured to determine an encoder used to generate a coded signal and selected from among multiple encoders comprising a silence encoder, a noise-like signal encoder, a time-domain encoder, and a transform-domain encoder, and to decode the coded signal based on a decoder complementary to the encoder used to generate the coded signal; and

a memory coupled to the at least one processor.

47. The apparatus of claim 46, wherein the at least one processor is configured to determine the encoder used to generate the coded signal based on encoder information sent with the coded signal.

48. A method comprising:

determining an encoder used to generate a coded signal and selected from among multiple encoders comprising a silence encoder, a noise-like signal encoder, a time-domain encoder, and a transform-domain encoder; and

decoding the coded signal based on a decoder complementary to the encoder used to generate the coded signal.