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, comprising:
receiving an encoded audio bitstream, the encoded audio bitstream including audio data and metadata audio signal including one or more sets of downmix loudness parameters;
determining if a first downmix loudness parameter indicates whether downmix loudness offset data exists, and if the downmix loudness offset data does exist, adjusting a difference between an expected loudness of a downmix audio signal and a measured loudness of the downmix audio signal based upon a second downmix loudness parameter; and
wherein the second downmix loudness parameter indicates whether there is a difference between the expected loudness of a 2-channel downmix output and an actual measured loudness.
2. The method of claim 1 wherein, the first downmix loudness parameter is a one-bit data field denoted as “dmixloudoffste” and the second downmix loudness parameter is a five-bit field denoted as “dmixloudoffst.”
3. The method of claim 2 , wherein the dmixloudoffst indicates whether there is a difference between the expected loudness of the 2-channel downmix output from an AC-3 or Enhanced AC-3 decoder, and the actual measured loudness, with all gain adjustments due to dialogue normalization, dynamic range compression and/or fixed attenuation to protect against downmix overload having been applied prior to measurement.
4. The method of claim 1 , wherein a program loudness data conveys data about program loudness, including measured loudness values for the program, and indication as to whether the loudness of the program has been corrected prior to AC-3 or Enhanced AC-3 encoding.
5. An audio processing apparatus comprising:
a buffer for storing at least a portion of an encoded audio bitstream, the encoded audio bitstream including audio data and metadata including one or more sets of downmix loudness parameters;
a demultiplexer for parsing the portion of the encoded audio bitstream; and
an audio decoder for decoding the audio data,
wherein the metadata includes a first downmix loudness parameter indicating whether downmix loudness offset data exists, and if the downmix loudness offset data does exist, a second downmix loudness parameter indicating whether there is a difference between an expected loudness of a 2-channel downmix of the audio data and an actual measured loudness of the 2-channel downmix of the audio data.
6. The audio processing apparatus of claim 5 , wherein, a first downmix loudness parameter is a one-bit data field denoted as “dmixloudoffste” and the second downmix loudness parameter is a five-bit field denoted as “dmixloudoffst.”
7. The audio processing apparatus of claim 5 , wherein the dmixloudoffst indicates whether there is a difference between the expected loudness of a 2-channel downmix output from an AC-3 or Enhanced AC-3 decoder, and an actual measured loudness, with all gain adjustments due to dialogue normalization, dynamic range compression and/or fixed attenuation to protect against downmix overload having been applied prior to measurement.
8. The audio processing apparatus of claim 5 , wherein a program loudness data conveys data about program loudness, including measured loudness values for the program, and indication as to whether the loudness of the program has been corrected prior to AC-3 or Enhanced AC-3 encoding.
9. A non-transitory computer-readable medium comprising machine executable instructions which, when executed, cause the machine to perform steps of:
receiving an encoded audio bitstream, the encoded audio bitstream including audio data and metadata audio signal including one or more sets of downmix loudness parameters;
determining if a first downmix loudness parameter indicates whether downmix loudness offset data exists, and if the downmix loudness offset data does exist, adjusting a difference between an expected loudness of a downmix audio signal and a measured loudness of the downmix audio signal based upon a second downmix loudness parameter; and
wherein the second downmix loudness parameter indicates whether there is a difference between the expected loudness of a 2-channel downmix output and an actual measured loudness.
10. The computer program product of claim 9 , wherein, the first downmix loudness parameter is a one-bit data field denoted as “dmixioudoffste” and the second downmix loudness parameter is a five-bit field denoted as “dmixioudoffst.”
11. The computer program product of claim 10 , wherein the dmixloudoffst indicates whether there is a difference between the expected loudness of the 2-channel downmix output from an AC-3 or Enhanced AC-3 decoder, and the actual measured loudness, with all gain adjustments due to dialogue normalization, dynamic range compression and/or fixed attenuation to protect against downmix overload having been applied prior to measurement.
12. The computer program product of claim 11 , wherein a program loudness data conveys data about program loudness, including measured loudness values for the program, and indication as to whether the loudness of the program has been corrected prior to AC-3 or Enhanced AC-3 encoding.