METADATA FOR LOUDNESS AND DYNAMIC RANGE CONTROL

• US 20140294200A1
• 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, Allamanche, Eric A., Strommer, Stefan K. O.
• Granted Patent: US 9,559,651 B2
• Time in Patent Office: Days
• US Class Current: 381/107
• 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 encoding audio signal, comprising:

applying an audio normalization gain value to an audio signal to produce a normalized signal; and

then

processing the normalized signal to compute a plurality of dynamic range control (DRC) gain values for the normalized signal, wherein the DRC gain values are computed in accordance with a selected one of a plurality of pre-defined DRC characteristics;

encoding the audio signal; and

providing the DRC gain values as metadata associated with the encoded audio signal.

2. The method of claim 1 further comprising:

providing an index of the selected DRC characteristic as metadata of the encoded audio signal.

3. The method of claim 1 wherein the audio normalization gain value is a program loudness normalization gain value.

4. The method of claim 1 wherein providing the DRC gain values as metadata comprises:

embedding the DRC gain values with the encoded audio signal into a primary data channel; and

providing the index of the selected DRC characteristic together with other metadata in an auxiliary data channel associated with the primary data channel.

5. The method of claim 4 wherein said other metadata comprises a program loudness value, and a True Peak value.

6. The method of claim 1 further comprising:

applying the DRC gain values to a signal derived from one of the audio signal or the normalized signal, to produce a dynamic range adjusted signal; and

performing audio measurement based on the dynamic range adjusted signal to compute a program loudness value; and

computing the audio normalization gain value using the program loudness value.

7. The method of claim 6 further comprising:

configuring a filter, based upon a characteristic of the audio signal and/or based upon a characteristic of a playback device that is expected to receive the encoded audio signal; and

pre-conditioning the dynamic range adjusted signal using the filter, prior to performing the audio measurement.

8. The method of claim 1 further comprising:

automatically selecting the audio normalization gain value based on a plurality of predetermined, target loudness values that are associated with a plurality of different types of audio content, respectively, in response to type of audio content in the audio signal.

9. A digital audio encoder apparatus, comprising:

a normalizer that is to apply an audio normalization gain value to an audio signal so as to produce a normalized audio signal;

a DRC processor that is to process the normalized audio signal to compute a plurality of dynamic range control (DRC) gain values for the normalized audio signal, wherein the DRC gain values are computed in accordance with a selected one of a plurality of pre-defined DRC characteristics;

an encoder to receive the audio signal; and

means for providing the DRC gain values as metadata associated with the encoded audio signal.

10. The apparatus of claim 9 further comprising means for providing an index of the selected DRC characteristic as metadata associated with the encoded audio signal.

11. The apparatus of claim 9 further comprising:

an audio measurement unit to compute loudness parameters based on the audio signal; and

means for providing the loudness parameters as metadata associated with the encoded signal.

12. The apparatus of claim 11 further comprising:

a downmix processor to compute a downmix of the audio signal, wherein the audio measurement unit is to compute the loudness parameters based on the downmix.

13. The apparatus of claim 11 further comprising a preconditioning filter through which the audio signal is to pass before being input to the audio measurement unit.

14. A method for decoding audio, comprising:

receiving an encoded audio signal;

receiving metadata associated with the encoded audio signal, the metadata including a plurality of dynamic range control (DRC) gain values;

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

selecting a current DRC characteristic from amongst a plurality of available DRC characteristics, and modifying the DRC gain values based on the current DRC characteristic; and

applying the modified DRC gain values to the decoded audio signal to produce a DRC adjusted audio signal.

15. The method of claim 14 wherein the received metadata further comprises an index of a previously selected DRC characteristic in accordance with which the DRC gain values were computed when the encoded audio signal was being generated, and wherein the selected current DRC characteristic is associated with the index.

16. The method of claim 14 wherein the received metadata further includes a plurality of values selected from the group consisting of:

program loudness, true peak, loudness range, maximum momentary loudness, and short-term loudness values.

17. The method of claim 14 wherein selecting the current DRC characteristic from amongst the plurality of available DRC characteristics is further based on one or more of the following:

user contexts including late night, walking, running, and car; and

speaker dynamic range.

18. A digital audio decoder apparatus, comprising:

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

a DRC processor that is to receive metadata which is associated with the encoded audio signal, wherein the metadata includes a plurality of dynamic range control (DRC) gain values, the DRC processor to select a current DRC characteristic from amongst a plurality of stored DRC characteristics and modify the DRC gain values based on the current DRC characteristic; and

a multiplier that is to apply the modified DRC gain values to the decoded audio signal to produce DRC adjusted audio signal.

19. The apparatus of claim 18 wherein the DRC processor is to receive further metadata, associated with the encoded audio signal, that comprises an index of a previously selected DRC characteristic in accordance with which the DRC gain values were computed when the encoded audio signal was being generated, and wherein the current DRC characteristic selected by the DRC processor is associated with the index.