Transient Detector and Method for Supporting Encoding of an Audio Signal

• US 20110046965A1
• Filed: 08/25/2008
• Published: 02/24/2011
• Est. Priority Date: 08/27/2007
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Ullberg, Gustaf, Taleb, Anisse
• Granted Patent: US 9,495,971 B2
• Time in Patent Office: Days
• US Class Current: 704/501
• 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. A transient detector operating on an audio signal, wherein said transient detector comprises:

means for 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; and

means for signaling said determined transient hangover indicator to an associated audio encoder to enable proper encoding of said following frame n+1.

2. The transient detector of claim 1, wherein said means for analyzing is 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 transient detector of claim 2, wherein said means for analyzing is configured to determine 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.

4. The transient detector of claim 2, wherein said means for analyzing 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 transient detector of claim 4, wherein said means for analyzing is configured to determine a transient hangover indicator indicating a transient for the following frame n+1 if 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 transient detector of claim 4, wherein said means for analyzing is configured to determine a hangover indicator that does not indicate a transient for the following frame n+1 if 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 transient detector 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 transient detector 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 a frame.

9. The transient detector of claim 4, wherein said transient detector comprises:

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

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

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

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

10. The transient detector of claim 2, wherein said means for analyzing 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 transient detector of claim 10, wherein said means for analyzing is configured to determine a transient hangover indicator indicating a transient for the following frame n+1 if the transient is located at the center or end of the given frame n.

12. The transient detector of claim 10, wherein said means for analyzing is configured to determine a transient hangover indicator that does not indicate a transient for the following frame n+1 if the transient is located at the beginning of the given frame n.

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

14. The transient detector 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. A method of supporting encoding of an audio signal, said method comprising the steps of:

receiving said audio signal;

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;

signaling said transient hangover indicator to an associated audio encoder to enable appropriate encoding actions with respect to said following frame n+1 of said audio signal.

16. The method of claim 15, 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.

17. The method of claim 16, 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.

18. The method of claim 16, 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.

19. The method of claim 18, 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.

20. The method of claim 16, 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.

21. The method of claim 15, wherein said signaling of said transient hangover indicator enables said audio encoder to perform, when a hangover indicator indicating a transient is signaled, encoding of said following frame n+1 in an encoding mode adapted for encoding of a frame that includes a transient.

22. The method of claim 21, wherein said encoding actions include, when a hangover indicator indicating a transient is signaled, decreasing the transform length to improve the time resolution of the transformation.

23. The method of claim 15, wherein said audio encoder is a transform-based encoder using a lapped transform.