System and method for non-destructively normalizing loudness of audio signals within portable devices
Many portable playback devices cannot decode and playback encoded audio content having wide bandwidth and wide dynamic range with consistent loudness and intelligibility unless the encoded audio content has been prepared specially for these devices. This problem can be overcome by including with the encoded content some metadata that specifies a suitable dynamic range compression profile by either absolute values or differential values relative to another known compression profile. A playback device may also adaptively apply gain and limiting to the playback audio. Implementations in encoders, in transcoders and in decoders are disclosed.
1. A method comprising:
receiving, by a decoding device, encoded audio information and metadata associated with an audio signal, the metadata including one or more parameter values specifying dynamic range compression (DRC) according to a first profile, and one or more differential coded parameter values;
applying, by the decoding device, a decoding process to the encoded audio information to obtain subband signals representing spectral content of the audio signal;
responsive to one or more control signals, modifying, by the decoding device, the subband signals using the one or more parameter values to obtain modified subband signals with changed dynamic range characteristics;
applying, by the decoding device, a synthesis filter bank to the modified subband signals to obtain a decoded audio signal;
computing one or more differential decoded parameter values as a sum of the one or more differential coded parameter values and one or more base parameter values; and
applying the one or more differential decoded parameter values to the decoded audio signal to adjust an amplitude of the decoded audio signal during playback.
2. The method of claim 1 , wherein the one or more differential coded parameter values specify DRC according to a second profile.
3. The method of claim 1 , wherein the metadata includes flags or bits that indicate whether a differential coded parameter value should be reused.
4. The method of claim 1 , wherein the one or more differential coded parameter values are configured to prevent a decoded audio signal sample from exceeding a reference reproduction level during playback.
5. The method of claim 1 , wherein the one or more control signals are included in the metadata.
6. The method of claim 1 , wherein the first profile includes one or more gain factors.
7. An apparatus comprising:
digital signal processor circuitry;
memory coupled to the digital signal processor circuitry and configured to store instructions, which when executed by the digital signal processor circuitry, cause the digital signal processor circuitry to perform operations comprising:
receiving encoded audio information and metadata associated with an audio signal, the metadata including one or more parameter values specifying dynamic range compression (DRC) according to a first profile, and one or more differential coded parameter values;
applying a decoding process to the encoded audio information to obtain subband signals representing spectral content of the audio signal;
responsive to one or more control signals, modifying, the subband signals using the one or more parameter values to obtain modified subband signals with changed dynamic range characteristics;
applying a synthesis filter bank to the modified subband signals to obtain a decoded audio signal;
computing one or more differential decoded parameter values as a sum of the one or more differential coded parameter values and one or more base parameter values; and
applying the one or more differential decoded parameter values to the decoded audio signal to adjust an amplitude of the decoded audio signal during playback.
8. The apparatus of claim 7 , wherein the one or more differential coded parameter values specify DRC according to a second profile.
9. The apparatus of claim 7 , wherein the metadata includes flags or bits that indicate whether a differential coded parameter value should be reused.
10. The apparatus of claim 7 , wherein the one or more control signals are included in the metadata.
11. The apparatus of claim 7 , wherein the first profile includes one or more gain factors.