ENCODED AUDIO EXTENDED METADATA-BASED DYNAMIC RANGE CONTROL

• US 20170032793A1
• Filed: 07/22/2016
• Published: 02/02/2017
• Est. Priority Date: 07/31/2015
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Baumgarte, Frank
• Granted Patent: US 9,837,086 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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: H04S 2400/13 Aspects of volume control, not necessarily automatic, in stereophonic sound systems
• CPC Class Codes: H04S 2400/15 Aspects of sound capture and related signal processing for recording or reproduction
• CPC Class Codes: H04S 2420/07 Synergistic effects of band splitting and sub-band processing
• CPC Class Codes: H04S 3/008 in which the audio signals are in digital form, i.e. employing more than two discrete digital channels data reduction aspects thereof based on psychoacoustics G10L19/02

Abstract

An audio encoder encodes a digital audio recording having a number of audio channels or audio objects. A Dynamic Range Control (DRC) processor produces a sequence of encoder DRC gain values, by applying a selected one of a number of DRC characteristics to a group of one or more of the audio channels or audio objects. The encoder DRC gain values are to be applied to adjust the group of audio channels or audio objects, upon decoding them from the encoded digital audio recording. A bitstream multiplexer combines a) the encoded digital audio recording with b) the sequence of encoder DRC gain values, an indication of the selected DRC characteristic, and an indication of an alternate DRC characteristic, the latter as metadata associated with the encoded digital audio recording. Other embodiments are also described including a system for decoding the encoded audio recording and performing DRC adjustment upon it.

Claims

1. A system for producing an encoded digital audio recording having a plurality of audio channels or audio objects, comprising:

an audio encoder to encode a digital audio recording having a plurality of audio channels or audio objects;

a Dynamic Range Control (DRC) processor to produce a sequence of encoder DRC gain values by applying a selected one of a plurality of DRC characteristics to a group of one or more of the plurality of audio channels or audio objects, wherein the encoder DRC gain values are to be applied to adjust the group of audio channels or audio objects upon decoding them from the encoded digital audio recording; and

means for providing as metadata associated with the encoded digital audio recording i) the sequence of encoder DRC gain values, ii) an indication of the selected DRC characteristic, and iii) an indication of an alternate DRC characteristic selected from the plurality of DRC characteristics.

2. The system of claim 1 wherein the metadata specifies a scenario or condition in which a decoding system is to apply DRC in accordance with the alternate DRC characteristic rather than the selected DRC characteristic.

3. The system of claim 1 wherein the metadata associated with the encoded digital audio recording is carried in a plurality of extension fields of MPEG-D DRC.

4. The system of claim 1 wherein the DRC processor is to receive the digital audio recording as input, and apply the input to a DRC application block that has been configured in accordance with the alternate DRC characteristic, to produce an alternate DRC-adjusted version of the digital audio recording,

wherein the system further comprises a loudness calculator to compute loudness information that gives a measure of loudness of the alternate DRC-adjusted version of the digital audio recording,

and wherein the means for providing as metadata associated with the encoded digital audio recoding includes the loudness information, for the alternate DRC-adjusted version, as part of the metadata.

5. The system of claim 1 wherein in the metadata, the indication of the alternate DRC characteristic comprises one of

a) an index or reference to a predetermined loudness vs. DRC gain curve or plot that is stored in a decoding system,

b) a plurality of constants or parameters that when inserted by the decoding system into a predefined mathematical function define a loudness vs. DRC gain curve,

c) a look up table of loudness and corresponding DRC gain values, or

d) a plurality of loudness and corresponding DRC gain values from which the decoding system interpolates a DRC gain value for an input loudness level.

6. The system of claim 1 wherein the DRC processor is to produce an encoder DRC gain set having a plurality of sequences of encoder DRC gain values,

and wherein the means for providing as metadata associated with the encoded digital audio recording also includes the encoded DRC gain set as part of the metadata,

and wherein the metadata specifies that one of the plurality of sequences of encoder DRC gain values is to be applied to adjust a plurality of sub-bands of an audio channel or audio object that has been decoded from the encoded digital audio recording.

7. The system of claim 6 wherein the metadata specifies that said one of the sequences of encoder DRC gain values is to be applied to all sub-bands of the decoded digital audio recording.

8. The system of claim 6 wherein the metadata specifies that 1) a first sub-band of the decoded digital audio recording is to be DRC adjusted by one of the sequences of encoder DRC gain values, and 2) a second sub-band is to be DRC adjusted by another one of the plurality of sequences of encoder DRC gain values.

9. The system of claim 6 wherein the metadata specifies 1) a first scaling value that is to be applied to scale the specified one of the sequences of DRC gain values before applying the scaled sequence to a first sub-band of the decoded audio channel or audio object, and 2) a second, different scaling value that is to be applied to scale the specified one of the sequences of encoder DRC gain values before applying the scaled sequence to a second sub-band of the decoded audio channel or audio object.

10. A system for producing a decoded digital audio recording, comprising:

a processor; and

memory having stored therein instructions that, when executed by the processor, cause the processor to;

receive a bitstream in which a digital audio recording has been encoded, and metadata associated with the digital audio recording, wherein the metadata includes a sequence of encoder DRC gain values, an indication of a selected DRC characteristic, wherein the sequence of encoder DRC gain values was derived based on applying the digital audio recoding to the selected DRC characteristic, and an indication of an alternate DRC characteristic,

decode the digital audio recoding, and

perform playback of the decoded recording by producing an alternate DRC-adjusted audio recording for playback, by

a) producing an inverse of the selected DRC characteristic using the indication, received in the metadata, of the selected DRC characteristic, and applying the sequence of encoder DRC gain values, received in the metadata, as input to said inverse to produce a sequence of loudness values,

b) using the indication, received in the metadata, of the alternate DRC characteristic, to obtain the alternate DRC characteristic, and applying the sequence of loudness values as input to the alternate DRC characteristic to produce an alternate sequence of DRC gain values, and

c) applying the alternate sequence of DRC gain values to the decoded digital audio recording to produce an alternate DRC-adjusted version of the digital audio recording.

11. The system of claim 10 wherein the metadata includes an encoder DRC gain set, the encoder DRC gain set having a plurality of sequences of encoder DRC gain values,

and wherein the metadata contains instructions in which an encoding system can specify that any one of the plurality of sequences of encoder DRC gain values can be applied to any sub-band of the decoded digital audio recording.

12. The system of claim 10 wherein the metadata includes an encoder DRC gain set, the encoder DRC gain set having a plurality of sequences of encoder DRC gain values,

and wherein the metadata contains instructions to the processor to apply a specified one of the sequences of encoder DRC gain values to a plurality of sub-bands of the decoded digital audio recoding when performing multi-band DRC.

13. The system of claim 10 wherein the metadata has instructions to the processor to 1) scale the specified one of the sequences of DRC gain values by a first scaling value as specified in the metadata, before applying the scaled sequence to a first sub-band of the decoded digital audio recording, and 2) scale the specified one of the sequences of DRC gain values by a second, different scaling value as specified in the metadata, before applying the scaled sequence to a second sub-band of the decoded digital audio recording.

14. A system for producing a decoded digital audio recording, comprising:

a processor;

a memory having instructions stored therein that, when executed by the processor, cause the processor to;

receive a bitstream in which a digital audio recording has been encoded, wherein the encoded digital audio recording is associated with metadata that includes an encoder DRC gain set having a plurality of sequences of encoder DRC gain values, decode the digital audio recording, and

perform multi-band DRC upon the decoded digital audio recording, wherein the metadata contains instruction to apply a specified one of the plurality of sequences of encoder DRC gain values that are in the metadata to a plurality of different sub-bands of the decoded digital audio recording, wherein the sub-bands are also specified in the metadata.

15. The system of claim 14 wherein the processor does not perform any grouping of audio channels or audio objects of the decoded audio recording, when performing multi-band DRC upon the decoded audio recording.

16. The system of claim 14 wherein the metadata specifies that said one of the sequences of encoder DRC gain values is to be applied to all of the sub-bands of the decoded digital audio recording.

17. The system of claim 14 wherein the metadata contains instructions to the processor to 1) scale the specified one of the sequences of DRC gain values by a first scaling value before applying the scaled sequence to a first sub-band, and 2) scale the specified one of the sequences of DRC gain values by a second scaling value before applying the scaled sequence to a second sub-band, wherein the first and second scaling values and the first and second sub-bands are specified in the metadata.

18. A method for producing an encoded digital audio recording, comprising:

encoding a digital audio recording that has a plurality of audio channels or audio objects;

producing a sequence of encoder DRC gain values by applying a selected one of a plurality of DRC characteristics to a group of one or more of the audio channels or audio objects, wherein the encoder DRC gain values are to be applied to adjust the group of audio channels or audio objects upon decoding them from the encoded digital audio recording; and

providing as metadata associated with the encoded digital audio recording (i) the sequence of encoder DRC gain values, (ii) an indication of the selected DRC characteristic and (iii) an indication of an alternate DRC characteristic selected from a plurality of DRC characteristics.

19. The method of claim 18 further comprising:

producing an alternate DRC-adjusted version of the digital audio recording in accordance with the alternate DRC characteristic;

computing loudness information that gives a measure of loudness of the alternate DRC-adjusted version of the digital audio recording; and

providing as part of said metadata associated with the encoded digital audio recording, the loudness information for the alternate DRC-adjusted version.

20. The method of claim 18 further comprising

providing as part of said metadata associated with the encoded digital audio recording, an instruction that the same sequence of encoder DRC gain values is to be applied by a decoding system to adjust a plurality of sub-bands of an audio channel or audio object that has been decoded from the encoded digital audio recording.

21. The method of claim 20 further comprising

providing as part of said metadata associated with the encoded digital audio recording, 1) a first scaling value and instruction to apply the first scaling value to scale the specified one of the sequences of DRC gain values before applying the scaled sequence to a first sub-band of the decoded audio channel or audio object, and 2) a second, different scaling value and instruction to apply the second scaling value to scale the specified one of the sequences of encoder DRC gain values before applying the scaled sequence to a second sub-band of the decoded audio channel or audio object.