Transient detector and method for supporting encoding of an audio signal

• US 9,495,971 B2
• Filed: 08/25/2008
• Issued: 11/15/2016
• Est. Priority Date: 08/27/2007
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Ullberg, Gustaf, Taleb, Anisse
• Primary Examiner(s): Lerner, Martin
• Application Number:
  US12/673,862
• Publication Number:
  US 20110046965A1
• Time in Patent Office: 3,004 Days
• Field of Search: 704/200.1, 704/205, 704/206, 704/211, 704/500, 704/501
• US Class Current: 1/1
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching

Abstract

A transient detector (100) analyzes (110) a given frame n of the input audio signal to determine, based on audio signal characteristics of the given frame n, a transient hangover indicator for a following frame n+1, and signals (120) the determined transient hangover indicator to an associated audio encoder (10) to enable proper encoding of the following frame n+1.

Claims

1. An apparatus comprising:

a transient detector circuitry configured to;

analyze a given frame n of an audio signal to determine, based on audio signal characteristics of said given frame n, a transient hangover indicator for an immediately following frame n+1 of said audio signal, the transient hangover indicator determined in response to determining that a power fluctuation in the given frame n of the audio signal exceeds a predetermined threshold, and

signal said determined transient hangover indicator to an associated audio encoder circuitry; and

the audio encoder circuitry encoding said following frame n+1,

wherein the transient detector circuitry analyzes the given frame n and determines the hangover indicator for the immediately following frame n+1 prior to encoding the immediately following frame n+1, and

wherein the power fluctuation in the given frame n of the audio signal is determined to exceed the predetermined threshold when a ratio of a short term power of the audio signal of the given frame n to a long term power of the audio signal of the given frame n exceeds the predetermined threshold.

2. The apparatus of claim 1, wherein the transient detector circuitry is further configured to determine the value of said transient hangover indicator for the following frame n+1 in dependence on the existence of audio signal characteristics representative of a transient in said given frame n.

3. The apparatus of claim 2, wherein the transient detector circuitry is configured to determine a transient hangover indicator indicating a transient for the following frame n+1 in response to determining that said audio signal characteristics of said given frame n includes characteristics representative of a transient.

4. The apparatus of claim 2, wherein the transient detector circuitry is configured to determine the value of said transient hangover indicator for the following frame n+1 also in dependence on a predetermined window function.

5. The apparatus of claim 4, wherein the transient detector circuitry is configured to determine a transient hangover indicator indicating a transient for the following frame n+1 in response to determining that said audio signal characteristics representative of a transient in said given frame n is detectable after a windowing operation based on said window function.

6. The apparatus of claim 4, wherein the transient detector circuitry is configured to determine a hangover indicator that does not indicate a transient for the following frame n+1 in response to determining that said audio signal characteristics representative of a transient in said given frame n is suppressed after a windowing operation based on said window function.

7. The apparatus of claim 4, wherein said window function corresponds to a window function used for transform coding of frame n of said audio signal in said associated audio encoder, but shifted one frame forward in time.

8. The apparatus of claim 7, wherein said associated audio encoder operates based on a lapped transform and associated window function using at least two frames for encoding frame n+1.

9. The apparatus of claim 4, wherein the transient detector circuitry is further configured to:

scale said given frame n by said window function to produce a first scaled frame;

determine a transient indicator for said given frame n based on the first scaled frame;

scale said given frame n by said window function shifted one frame forward in time to produce a second scaled frame; and

determine a transient hangover indicator for said following frame n+1 based on the second scaled frame.

10. The apparatus of claim 2, wherein the transient detector circuitry is configured to determine the value of said transient hangover indicator for the following frame n+1 also in dependence on the location of the transient in said given frame n.

11. The apparatus of claim 10, wherein the transient detector circuitry is configured to determine a transient hangover indicator indicating a transient for the following frame n+1 in response to determining that the transient is located at the center or end of the given frame n.

12. The apparatus of claim 10, wherein the transient detector circuitry is configured to determine a transient hangover indicator that does not indicate a transient for the following frame n+1 in response to determining that the transient is located at the beginning of the given frame n.

13. The apparatus of claim 1, wherein said transient detector circuitry is intended for operation with a transform-based audio encoder using a lapped transform.

14. The apparatus of claim 1, wherein said proper encoding of said following frame n+1 includes transient encoding if a transient hangover indicator indicating a transient is signaled.

15. The apparatus of claim 1, wherein the transient hangover indicator indicates one of a true and false value.

16. The apparatus according to claim 1, wherein the n+1 frame is an input to the audio encoding circuitry, and the audio encoding circuitry is further configured to encode the n+1 frame in response to receiving said transient hangover indicator from the transient detector circuitry.

17. The apparatus according to claim 1, wherein the audio encoding circuitry is further configured to encode the n+1 frame based on at least one characteristic of said given frame n.

18. The apparatus according to claim 1, wherein the audio encoding circuitry is further configured to encode the n+1 frame in accordance with a frequency domain transform.

19. The apparatus according to claim 1, wherein the transient detector circuitry is configured to determine a hangover indicator that does not indicate a transient for the following frame n+1 in response to determining that said audio signal characteristics representative of a transient in said given frame n is suppressed after a windowing operation based on a predetermined window function.

20. The apparatus according to claim 1, wherein the transient detector circuitry is configured to determine a transient hangover indicator that does not indicate a transient for the following frame n+1 in response to determining that the transient is located at the beginning of the given frame n.

21. A method of supporting encoding of an audio signal, said method comprising the steps of:

receiving said audio signal at an audio encoding circuitry comprising an audio encoder;

the audio encoding circuitry analyzing a given frame n of said audio signal to determine, based on audio signal characteristics of said given frame n, a transient hangover indicator for a following frame n+1, the transient hangover indicator determined in response to determining that a power fluctuation in the given frame n of the audio signal exceeds a predetermined threshold; and

said audio encoder using said determined transient hangover indicator in encoding said following frame n+1,

wherein the transient detector circuitry analyzes the given frame n and determines the hangover indicator for the immediately following frame n+1 prior to encoding the immediately following frame n+1, and

wherein the power fluctuation in the given frame n of the audio signal is determined to given frame n to the a long term power of the audio signal of the given frame n exceeds the predetermined threshold.

22. The method of claim 21, wherein said step of analyzing comprises the step of determining the value of said transient hangover indicator for the following frame n+1 in dependence on the existence of audio signal characteristics representative of a transient in said given frame n.

23. The method of claim 22, wherein said step of analyzing comprises the step of determining a transient hangover indicator indicating a transient for the following frame n+1 if said audio signal characteristics of said given frame n includes characteristics representative of a transient.

24. The method of claim 22, wherein said step of analyzing comprises the step of determining the value of said transient hangover indicator for the following frame n+1 also in dependence on a predetermined window function.

25. The method of claim 24, wherein said window function corresponds to a window function used for transform coding of frame n of said audio signal in said associated audio encoder, but shifted one frame forward in time.

26. The method of claim 22, wherein said step of analyzing comprises the step of determining the value of said transient hangover indicator for the following frame n+1 also in dependence on the location of the transient in said given frame n.

27. The method of claim 21, wherein the step of using said transient hangover indicator in encoding said following frame n+1 comprises:

selecting an encoding mode from a set of two or more encoding modes based on the value of said transient hangover indicator, said set of two or more encoding modes comprising a transient encoding mode and a non-transient encoding mode, and

encoding said following frame n+1 using said selected encoding mode.

28. The method of claim 27, wherein

said selecting step comprises selecting the transient encoding mode in response to determining that the transient hangover indicator indicates that a transient was detected in frame n, and

said step of encoding said following frame n+1 using said transient encode mode comprises using a decreased transform length to improve the time resolution of the transformation.

29. The method of claim 21, wherein said audio encoder is a transform-based encoder using a lapped transform.

30. The method of claim 21, further comprising:

setting the value of said transient hangover indicator for the following frame n+1 in dependence on the existence of audio signal characteristics representative of a transient in said given frame n and also in dependence on a predetermined window function, wherein

the step of setting the value comprises setting the value such that the hangover indicator does not indicate a transient for the following frame n+1 in response to determining that said audio signal characteristics representative of a transient in said given frame n is suppressed after a windowing operation based on said window function.

31. The method of claim 21, further comprising:

setting the value of said transient hangover indicator for the following frame n+1 in dependence on the existence of audio signal characteristics representative of a transient in said given frame n and also in dependence on a predetermined window function, wherein

said window function corresponds to a window function used for transform coding of frame n of said audio signal in said associated audio encoder, but shifted one frame forward in time, and

said audio encoder operates based on a lapped transform and associated window function using at least two frames for encoding frame n+1.

32. The method of claim 21, further comprising:

scaling said given frame n by a window function to produce a first scaled frame;

determining a transient indicator for said given frame n based on the first scaled frame;

scaling said given frame n by said window function shifted one frame forward in time to produce a second scaled frame; and

determining a transient hangover indicator for said following frame n+1 based on the second scaled frame.

33. The method of claim 21, further comprising:

setting the value of said transient hangover indicator for the following frame n+1 in dependence on the existence of audio signal characteristics representative of a transient in said given frame n and also in dependence on the location of the transient in said given frame n; and

determining a transient hangover indicator that does not indicate a transient for the following frame n+1 in response to determining that the transient is located at the beginning of the given frame n.

34. The method of claim 21, wherein the transient hangover indicator indicates one of a true and false value.