METHODS AND SYSTEMS FOR AVOIDING PARTIAL COLLAPSE IN MULTI-BLOCK AUDIO CODING

• US 20120232908A1
• Filed: 03/07/2012
• Published: 09/13/2012
• Est. Priority Date: 03/07/2011
• Status: Active Grant

• Current Assignee: Jean-Marc Valin, Timothy B. Terriberry
• Original Assignee: Jean-Marc Valin, Timothy B. Terriberry
• Inventors: Terriberry, Timothy B., Valin, Jean-Marc
• Granted Patent: US 9,015,042 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/028 Noise substitution, i.e. substituting non-tonal spectral components by noisy source comfort noise for discontinuous speech transmission G10L19/012
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering

Abstract

Embodiments are described of a multi-block coding scheme for an audio signal to prevent partial collapse conditions from causing pre-echo compression artifacts. An audio codec includes a segmentation component partitioning the audio signal into a plurality of tiles, wherein each tile comprises data from a particular segment of time and a particular set of frequencies of the audio signal; a band energy component determining an energy value for each tile corresponding to a signal component in a respective tile; an encoder flag tracking component marking a tile as not collapsed or collapsed based on the energy value in that tile; and a decoder flag tracking component filling all tiles marked as collapsed with pseudorandom noise at an estimated energy level.

Claims

1. A method of coding an audio signal, comprising:

partitioning the audio signal into a plurality of tiles, wherein each tile comprises data from a particular segment of time and a particular set of frequencies of the audio signal;

determining an energy value for each tile corresponding to a signal component in a respective tile;

marking a tile as not collapsed or collapsed based on the energy value in that tile; and

filling all tiles marked as collapsed with pseudorandom noise.

2. The method of claim 1 wherein the pseudorandom noise for a tile of a current frame is selected to be of an energy level that is dependent upon an energy level of a same band of the plurality of tiles in a frame prior to the current frame.

3. The method of claim 2 further comprising:

setting an feature enable bit to indicate that a collapsed tile is to be filled with pseudorandom noise; and

transmitting the feature enable bit as part of the bitstream between the encoder circuit and the decoder circuit, wherein the decoder circuit fills the collapsed tile with the pseudorandom noise.

4. The method of claim 1 wherein at least some of the plurality of tiles are subject to a defined change of a time-frequency resolution of each respective tile that causes to tile to increase either a time (T) resolution of the respective band or a frequency (F) resolution of the respective tile.

5. The method of claim 4, wherein in the case that the time-frequency resolution is changed to increase the time resolution and increase a number of tiles in a frame of the audio signal, each resulting tile is marked with the identical flag state of an original tile that the resulting tiles are derived from, such that the resulting tiles are marked as not collapsed if the original tile is marked as not collapsed, or the resulting tiles are marked as collapsed if the original tile is marked as collapsed.

6. The method of claim 4, wherein in the case that the time-frequency resolution is changed to decrease the time resolution, the resulting tile is marked as not collapsed if any original tile from which the resulting tile is formed is marked as not collapsed, and the resulting tile is marked as collapsed only if all of the original tiles from which the resulting tile is formed are marked as collapsed.

7. A method of coding an audio signal to reduce compression artifacts in an audio codec, comprising:

dividing frames of the audio signal into a plurality of tiles, wherein each tile comprises data from a particular segment of time and a particular set of frequencies of the audio signal;

combining or separating the tiles into tile partitions based on a variable time-frequency resolution method;

determining whether or not any of the tile partitions represents a hole in a frame of the audio signal due to insufficient bits available to code a particular tile partition by examining a state of a frequency coefficient derived for the particular tile; and

filling any tile partition that does not contain a non-zero frequency coefficient with pseudorandom noise.

8. The method of claim 7 wherein the pseudorandom noise for a filled tile partition of a current frame is selected to be of an energy level that is dependent upon an energy level of a same band of a frame prior to the current frame.

9. The method of claim 8 further comprising:

setting an feature enable bit to indicate that a zero frequency coefficient tile partition is to be filled with pseudorandom noise; and

transmitting the feature enable bit as part of a bitstream transmitted between an encoder circuit and a decoder circuit of an audio code, wherein the decoder circuit fills the collapsed tile with the pseudorandom noise.

10. The method of claim 9 further comprising, if the feature enable bit is set:

setting a flag to indicate whether a particular tile partition is not collapsed, wherein the flag is set to a not collapsed state if the particular tile partition contains a non-zero frequency coefficient; and

encoding the flag in a bitstream transmitted between an encoder circuit and a decoder circuit of the audio codec, wherein the flag comprises a single bit assigned to each tile partition of a plurality of tile partitions in the current frame.

11. The method of claim 10, wherein in the case that the time-frequency resolution is changed to increase the time resolution and increase a number of tiles in a frame of the audio signal, each resulting tile partition is marked with the identical flag state of an original tile from which the resulting tile partitions are derived.

12. The method of claim 10, wherein in the case that the time-frequency resolution is changed to decrease the time resolution, the resulting tile partition is marked as not collapsed if any original tile from which the resulting tile partition is formed is marked as not collapsed, and the resulting tile partition is marked as collapsed only if all of the original tiles from which the resulting tile partition is formed are marked as collapsed.

13. A system for coding an audio signal in an audio codec, comprising:

a segmentation component partitioning the audio signal into a plurality of tiles, wherein each tile comprises data from a particular segment of time and a particular set of frequencies of the audio signal;

a band energy component determining an energy value for each tile corresponding to a signal component in a respective tile;

an encoder flag tracking component marking a tile as not collapsed or collapsed based on the energy value in that tile; and

a decoder flag-tracking component filling all tiles marked as collapsed with pseudorandom noise.

14. The system of claim 13 wherein the pseudorandom noise for a tile of a current frame is selected to be of an energy level that is dependent upon an energy level of a same band of the plurality of tiles in a frame prior to the current frame.

15. The system of claim 14 further comprising:

a selection component setting an feature enable bit to indicate that a collapsed tile is to be filled with pseudorandom noise; and

a transmitter of the encoder transmitting the feature enable bit as part of the bitstream between the encoder circuit and the decoder circuit, wherein the decoder circuit fills the collapsed tile with the pseudorandom noise.

16. The system of claim 13 wherein at least some of the plurality of tiles are subject to a defined change of a time-frequency resolution of each respective tile that causes to tile to increase either a time (T) resolution of the respective band or a frequency (F) resolution of the respective tile.

17. The system of claim 16, wherein in the case that the time-frequency resolution is changed to increase the time resolution and increase a number of tiles in a frame of the audio signal, each resulting tile is marked with the identical flag state of an original tile that the resulting tiles are derived from, such that the resulting tiles are marked as not collapsed if the original tile is marked as not collapsed, or the resulting tiles are marked as collapsed if the original tile is marked as collapsed.

18. The system of claim 16, wherein in the case that the time-frequency resolution is changed to decrease the time resolution, the resulting tile is marked as not collapsed if any original tile from which the resulting tile is formed is marked as not collapsed, and the resulting tile is marked as collapsed only if all of the original tiles from which the resulting tile is formed are marked as collapsed.