Metadata for loudness and dynamic range control

• US 10,644,666 B2
• Filed: 01/27/2017
• Issued: 05/05/2020
• Est. Priority Date: 03/29/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Baumgarte, Frank, Allamanche, Eric A., Strommer, Stefan K. O.
• Primary Examiner(s): Truong, Kenny H
• Application Number:
  US15/417,424
• Publication Number:
  US 20170201219A1
• Time in Patent Office: 1,194 Days
• Field of Search: None
• 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 21/0316 by changing the amplitude
• CPC Class Codes: H03G 3/20 Automatic control H03G3/005 takes precedence; combined with volume compression or expansion H03G7/00
• CPC Class Codes: H03G 7/007 of digital or coded signals

Abstract

An audio normalization gain value is applied to an audio signal to produce a normalized signal. The normalized signal is processed to compute dynamic range control (DRC) gain values in accordance with a selected one of several pre-defined DRC characteristics. The audio signal is encoded, and the DRC gain values are provided as metadata associated with the encoded audio signal. Several other embodiments are also described and claimed.

Claims

1. A method for audio playback processing, comprising:

receiving an encoded audio file and metadata associated therewith, wherein the metadata includes i) a set of loudness parameters that include program loudness of a downmixed version of the encoded audio file and ii) DRC parameters, wherein the program loudness is an audio measurement of an average loudness estimate of the entire content of the downmixed version of the encoded audio file;

decoding the encoded audio file to produce a decoded audio signal;

processing the decoded audio signal to produce a downmix;

performing dynamic range adjustments i) upon the downmix or ii) upon the decoded audio signal prior to downmix, in accordance with the DRC parameters in the metadata; and

adjusting the downmix based on the program loudness in the metadata.

2. The method of claim 1 wherein the set of loudness parameters include true peak and wherein adjusting the downmix is further based on the true peak and on user input.

3. The method of claim 1 wherein the set of loudness parameters also includes loudness range, maximum momentary loudness, and short-term loudness values.

4. The method of claim 1 wherein the metadata contains an index of a previously selected DRC characteristic in accordance with which the DRC parameters were computed, the method further comprising:

selecting a current DRC characteristic from amongst a plurality of available DRC characteristics, wherein the selected current DRC characteristic is associated with the index; and

producing modified DRC gain values based on the current DRC characteristic by i) applying the plurality of DRC parameters from the metadata to the current DRC characteristic to obtain a plurality of input levels, ii) selecting a target DRC characteristic from amongst the plurality of available DRC characteristics, and iii) applying the plurality of input levels obtained in i) to the target DRC characteristic,

wherein performing dynamic range adjustments upon the downmix comprises applying the modified DRC gain values to the downmix.

5. The method of claim 4 wherein selecting the target DRC characteristic from amongst the plurality of available DRC characteristics is further based on one or more of a) a user context or b) speaker signal path dynamic range, wherein the user context is one of late night, walking, running, or car.

6. The method of claim 1 wherein the metadata contains i) downmix gains that were used to produce the downmixed version of the encoded audio file, and ii) anchor loudness of the downmixed version of the encoded audio file.

7. The method of claim 1 wherein the metadata contains i) downmix gains that were used to produce the downmixed version of the encoded audio file, and ii) true peak of the downmixed version of the encoded audio file.

8. A digital audio decoder apparatus, comprising:

a decoder to receive an encoded audio signal file and produce a decoded audio signal; and

a downmix processor to receive the decoded audio signal and a set of loudness parameters extracted from metadata that is associated with the encoded audio file wherein the set of loudness parameters includes program loudness of a downmixed version of the encoded audio file, the program loudness is an audio measurement of an average loudness estimate of the entire content of the downmixed version of the encoded audio file, wherein the downmix processor is to produce a downmixed audio signal;

a DRC processor to produce DRC gain values in accordance with DRC parameters that are extracted from the metadata that is associated with the encoded audio file; and

a multiplier to adjust i) the downmixed audio signal or ii) the decoded audio signal prior to downmix, in accordance with the DRC gain values produced by the DRC processor;

a processor to adjust the downmixed audio signal based on the program loudness in the metadata and based on a target loudness; and

a digital to analog converter (DAC) to convert the adjusted downmixed audio signal into analog form during playback of the encoded audio file.

9. The digital audio decoder apparatus of claim 8 wherein the set of loudness parameters is one of a) a first set that describes loudness profile of a respective downmix or b) a second set that describes loudness profile of a base channel layout.

10. The digital audio decoder apparatus of claim 8 wherein the set of loudness parameters include true peak.

11. The digital audio decoder apparatus of claim 8 wherein the metadata contains an index of a previously selected DRC characteristic in accordance with which the DRC parameters were computed,

wherein the DRC processor to select a current DRC characteristic, from amongst a plurality of stored DRC characteristics, that is associated with the index, and produce modified DRC gain values based on i) applying the DRC parameters from the metadata to the current DRC characteristic to obtain a plurality of input levels, ii) selecting a target DRC characteristic from amongst the plurality of stored DRC characteristics, and iii) applying the plurality of input levels obtained in i) to the target DRC characteristic, and

wherein the multiplier is to adjust the downmixed audio signal in accordance with the modified DRC gain values produced by the DRC processor.

12. The digital audio decoder apparatus of claim 11 wherein the DRC processor is to select the target DRC characteristic from amongst the plurality of stored DRC characteristics based on one or more of the following:

playback volume setting;

user context including late night, walking, running, or car;

DAC dynamic range; and

speaker dynamic range.