METADATA DRIVEN DYNAMIC RANGE CONTROL

• US 20140297291A1
• Filed: 03/26/2014
• Published: 10/02/2014
• Est. Priority Date: 03/29/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Baumgarte, Frank M.
• Granted Patent: US 9,607,624 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/167 Audio streaming, i.e. formatting and decoding of an encoded audio signal representation into a data stream for transmission or storage purposes
• CPC Class Codes: H03G 7/002 in untuned or low-frequency amplifiers, e.g. audio amplifiers H03G7/007, H03G7/001, H03G7/008, H03G7/02, H03G7/06 take precedence
• CPC Class Codes: H03G 7/007 of digital or coded signals

Abstract

A system for encoding and applying Dynamic Range Control/Compression (DRC) gain values to a piece of sound program content is described. In particular, a set of DRC gain values representing a DRC gain curve for the piece of content may be divided into frames corresponding to frames of the piece of content. A set of fields may be included with an audio signal representing the piece of content. The additional fields may represent the DRC gain values using linear or spline interpolation. The additional fields may include 1) an initial gain value for each DRC frame, 2) a set of slope values at particular points in the DRC curve, 3) a set of time delta values for each consecutive pair of slope values, and/or 4) one or more gain delta values representing changes of DRC gain values in the DRC gain curve between points of the slope values.

Claims

1. A method of encoding Dynamic Range Control (DRC) gain values in a bitstream representing a piece of sound program content, comprising:

grouping each audio channel of the sound program content into a single DRC group from a set of DRC groups;

encoding DRC gain values into DRC gain data for each DRC sub-band in each audio frame for each DRC group; and

inserting the DRC gain data into the bitstream for each DRC group.

2. The method of claim 1, wherein the DRC gain data is organized in DRC frames with a size equal to the size of the audio frames in the DRC groups.

3. The method of claim 1, wherein the maximum sample rate of the DRC gain data used to encode the DRC gain values is an integer power of two relative to the sample interval of the sound program content.

4. The method of claim 3, wherein the minimum sample interval for the DRC gain data is between ½

and 1.0 ms.

5. The method of claim 2, further comprising:

inserting a coding mode data value into the bitstream for each DRC group, wherein the coding mode data value represents a mode for encoding the DRC gain values in each corresponding DRC frame.

6. The method of claim 5, wherein the coding mode indicates the number of DRC gain values for a DRC group.

7. The method of claim 5, further comprising:

inserting an initial gain value into the bitstream for each DRC frame, wherein the initial gain value indicates the starting DRC gain value that is used to generate subsequent DRC gain values in a corresponding DRC frame.

8. The method of claim 7, further comprising:

inserting a time delta value into the bitstream for pairs of DRC gain values, wherein the time delta value indicates a time separation between each pair of DRC gain values; and

inserting a gain delta value into the bitstream for pairs of DRC gain values, wherein the gain delta value indicates DRC gain value differences between each pair of DRC gain values.

9. The method of claim 7, further comprising:

inserting slope values into the bitstream for each DRC frame, wherein the slope values correspond to sampled points of a DRC gain curve representing the DRC gain values.

10. The method of claim 8, wherein a time delta value and a gain delta value are used by an audio playback device to apply DRC gain to a corresponding audio frame using interpolation.

11. The method of claim 10, wherein the interpolation is a linear interpolation or a window-based overlap-add interpolation.

12. The method of claim 10, wherein the audio playback device further uses a slope value to apply DRC gain to a corresponding audio frame using interpolation.

13. The method of claim 12, wherein a slope value, a time delta value, and again delta value are inserted at the end of each DRC frame to allow use of a low-delay mode during decoding by the playback device.

14. The method of claim 12, wherein the interpolation is a cubic interpolation.

15. The method of claim 12, wherein the interpolation is a spline interpolation.

16. The method of claim 1, wherein multiple channels are assigned to a single DRC group.

17. The method of claim 8, wherein the time delta values are Huffman encoded.

18. A method for applying Dynamic Range Control (DRC) gain values to a piece of sound program content, comprising:

gathering multi-band DRC configuration information, wherein the multi-band DRC configuration information indicates the number of independent DRC gain sequences in the bitstream and the number of DRC channel groups in the bitstream for the entire band or multiple DRC sub-bands;

parsing the bitstream to retrieve quantized data values representing DRC gain values for each DRCgain frame;

decoding the quantized data values using code tables to generate the DRC gain data;

decoding the DRC gain data to generate DRC gain values to be applied to corresponding audio frames of the piece of sound program content; and

applying the DRC gain values to the entire band or multiple sub-bands of each audio frame.

19. The method of claim 18, wherein the DRC configuration information is gathered from a header of the bitstream.

20. The method of claim 18, further comprising:

extracting a coding mode data value from the bitstream for each DRC gain frame in each DRC channel group, wherein the coding mode data value represents an encoding mode of the DRC gain values in each corresponding DRC gain frame.

21. The method of claim 20, further comprising:

extracting an initial gain value from the bitstream for each DRC gain frame, wherein the initial gain value is used to apply gain to a first segment of a corresponding audio frame.

22. The method of claim 20, further comprising:

extracting one or more time delta values from the bitstream, wherein each of the time delta values indicate a time separation between pairs of DRC gain values; and

extracting one or more gain delta values from the bitstream, wherein the gain delta values indicate DRC gain value differences between pairs of DRC gain values.

23. The method of claim 22, further comprising:

extracting slope values from the bitstream for each DRC gain frame, wherein the slope values correspond to sampled points of a DRC gain curve representing the DRC gain values.

24. The method of claim 22, further comprising:

generating a DRC gain value for the first segment of an audio frame based on the initial gain value for a corresponding DRC gain frame; and

generating DRC gain values for a second segment of the audio frame using interpolation based on the DRC gain value generated for the first segment, time delta values, and gain delta values associated with the first and second segments.

25. The method of claim 18, further comprising:

filtering the audio signal to split each audio frame into multiple sub-bands.

26. The method of claim 22, wherein the interpolation is a linear interpolation or a window-based overlap-add interpolation.

27. The method of claim 23, further comprising:

generating a DRC gain value for the first segment of an audio frame based on the initial gain value for a corresponding DRC gain frame; and

generating DRC gain values for a second segment of the audio frame using interpolation based on the DRC gain value generated for the first segment, a slope value, time delta values, and gain delta values associated with the first and second segments.

28. The method of claim 27, wherein the interpolation is a spline interpolation.