Loudness adjustment for downmixed audio content
Audio content coded for a reference speaker configuration is downmixed to downmix audio content coded for a specific speaker configuration. One or more gain adjustments are performed on individual portions of the downmix audio content coded for the specific speaker configuration. Loudness measurements are then performed on the individual portions of the downmix audio content. An audio signal that comprises the audio content coded for the reference speaker configuration and downmix loudness metadata is generated. The downmix loudness metadata is created based at least in part on the loudness measurements on the individual portions of the downmix audio content.
1. A method for gain adjusting audio signals based on encoder-generated loudness metadata, the method comprising:
receiving, by an audio decoder operating in a playback channel configuration different from a reference channel configuration, an audio signal for the reference channel configuration, the audio signal including audio sample data for each channel of the reference channel configuration, and the encoder-generated loudness metadata, the encoder-generated loudness metadata comprising loudness metadata for a plurality of channel configurations including the playback channel configuration and the reference channel configuration;
downmixing the audio sample data into downmixed audio sample data for the audio channels of the playback channel configuration;
selecting, from the loudness metadata for the plurality of channel configurations, the loudness metadata for the playback channel configuration;
determining loudness adjustment gains from the loudness metadata for the playback channel configuration; and
applying the loudness adjustment gains as a part of overall gains applied to the downmixed audio sample data to generate output audio sample data for each channel of the playback channel configuration;
wherein the loudness adjustment gains depend on a loudness level indicated by the loudness metadata for the playback channel configuration and a reference loudness level.
2. A non-transitory computer readable storage medium, storing software instructions, which when executed by one or more processors cause performing:
receiving, by an audio decoder operating in a playback channel configuration different from a reference channel configuration, an audio signal for the reference channel configuration, the audio signal including audio sample data for each channel of the reference channel configuration, and encoder-generated loudness metadata, the encoder-generated loudness metadata comprising loudness metadata for a plurality of channel configurations including the playback channel configuration and the reference channel configuration;
downmixing the audio sample data into downmixed audio sample data for the audio channels of the playback channel configuration;
selecting, from the loudness metadata for the plurality of channel configurations, the loudness metadata for the playback channel configuration;
determining loudness adjustment gains from the loudness metadata for the playback channel configuration; and
applying the loudness adjustment gains as a part of overall gains applied to the downmixed audio sample data to generate output audio sample data for each channel of the playback channel configuration;
wherein the loudness adjustment gains depend on a loudness level indicated by the loudness metadata for the playback channel configuration and a reference loudness level.
3. An audio signal processing device for gain adjusting audio signals based on encoder-generated loudness metadata, wherein the audio signal processing device:
receives, by an audio decoder operating in a playback channel configuration different from a reference channel configuration, an audio signal for the reference channel configuration, the audio signal including audio sample data for each channel of the reference channel configuration, and the encoder-generated loudness metadata, the encoder-generated loudness metadata comprising loudness metadata for a plurality of channel configurations including the playback channel configuration and the reference channel configuration;
downmixing the audio sample data into downmixed audio sample data for the audio channels of the playback channel configuration;
selects, from the loudness metadata for the plurality of channel configurations, the loudness metadata for the playback channel configuration;
determines loudness adjustment gains from the loudness metadata for the playback channel configuration; and
applies the loudness adjustment gains as a part of overall gains applied to the downmixed audio sample data to generate output audio sample data for each channel of the playback channel configuration;
wherein the loudness adjustment gains depend on a loudness level indicated by the loudness metadata for the playback channel configuration and a reference loudness level.