Method for correcting metadata affecting the playback loudness and dynamic range of audio information
A coded signal conveys encoded audio information and metadata that may be used to control the loudness and dynamic range of the audio information during its playback. If the values for these metadata parameters are set incorrectly, annoying fluctuations in loudness during playback can result. The present invention overcomes this problem by detecting incorrect metadata parameter values in the signal and replacing the incorrect values with corrected values.
1. A method for correcting playback loudness and dynamic range of audio information, wherein the method comprises steps that:
receive an input signal that conveys data representing a first loudness normalization level, a first dynamic range adjustment level and first encoded audio information, wherein the data conveyed by the input signal was produced by an encoding process that generated the first encoded audio information according to psychoacoustic principles and determined the first dynamic range adjustment level in response to audio information amplitude, the first loudness normalization level and a compression profile specifying one or more operational characteristics of a signal compressor;
obtain decoded audio information from an application of a decoding process to the input signal;
obtain a measure of loudness from an analysis of the decoded audio information and derive a second loudness normalization level from the measure of loudness;
obtain an estimate of the compression profile used by the encoding process from an analysis of the decoded audio information and from the first dynamic range adjustment level;
generate an output signal that conveys data representing a third loudness normalization level, a third dynamic range adjustment level and third encoded audio information representing the audio information in an encoded form, wherein:
if a difference between the first and second loudness normalization levels does not exceed a threshold, the third loudness level represents the first loudness normalization level, the third dynamic range adjustment level represents the first dynamic range adjustment level and the third encoded audio information represents the first encoded audio information, and
if the difference between the first and second loudness normalization levels exceeds the threshold, the third loudness level is derived from the second loudness normalization level and the third dynamic range adjustment level is obtained in response to the audio information amplitude, the third loudness normalization level and the estimate of the compression profile.
2. The method of claim 1 wherein, if the difference between the first and second loudness normalization levels exceeds the threshold, the third encoded audio information is generated by encoding the decoded audio information according to psychoacoustic principles.
3. The method of claim 1 wherein, if the difference between the first and second loudness normalization levels exceeds the threshold, the third encoded audio information represents the first encoded audio information.
4. The method of claim 1 wherein the input signal conveys a first number of bits representing the first dynamic range adjustment level and the output signal is generated with data rearranged to accommodate a second number of bits representing the third dynamic range adjustment level, wherein the first number of bits is greater than the second number of bits.
5. The method of claim 1 wherein the input signal conveys a first number of bits representing the first dynamic range adjustment level and the output signal is generated with data rearranged to accommodate a second number of bits representing the third dynamic range adjustment level, wherein the First number of bits is less than the second number of bits.
6. An apparatus for correcting playback loudness and dynamic range of audio information, wherein the apparatus comprises:
means for receiving an input signal that conveys data representing a first loudness normalization level, a first dynamic range adjustment level and first encoded audio information, wherein the data conveyed by the input signal was produced by an encoding process that generated the first encoded audio information according to psychoacoustic principles and determined the first dynamic range adjustment level in response to audio information amplitude, the first loudness normalization level and a compression profile specifying one or more operational characteristics of a signal compressor;
means for obtaining decoded audio information from an application of a decoding process to the input signal;
means for obtaining a measure of loudness from an analysis of the decoded audio information and derive a second loudness normalization level from the measure of loudness;
means for obtaining an estimate of the compression profile used by the encoding process from an analysis of the decoded audio information and from the first dynamic range adjustment level;
means for generating an output signal that conveys data representing a third loudness normalization level, a third dynamic range adjustment level and third encoded audio information representing the audio information in an encoded form, wherein:
if a difference between the first and second loudness normalization levels does not exceed a threshold, the third loudness level represents the first loudness normalization level, the third dynamic range adjustment level represents the first dynamic range adjustment level and the third encoded audio information represents the first encoded audio information, and
if the difference between the first and second loudness normalization levels exceeds the threshold, the third loudness level is derived from the second loudness normalization level and the third dynamic range adjustment level is obtained in response to the audio information amplitude, the third loudness normalization level and the estimate of the compression profile.
7. A computer-readable medium recording a program of instructions that is executable by a processor to perform a method for correcting playback loudness and dynamic range of audio information, wherein the method comprises steps that:
receive an input signal that conveys data representing a first loudness normalization level, a first dynamic range adjustment level and first encoded audio information, wherein the data conveyed by the input signal was produced by an encoding process that generated the first encoded audio information according to psychoacoustic principles and determined the first dynamic range adjustment level in response to audio information amplitude, the first loudness normalization level and a compression profile specifying one or more operational characteristics of a signal compressor;
obtain decoded audio information from an application of a decoding process to the input signal;
obtain a measure of loudness from an analysis of the decoded audio information and derive a second loudness normalization level from the measure of loudness;
obtain an estimate of the compression profile used by the encoding process from an analysis of the decoded audio information and from the first dynamic range adjustment level;
generate an output signal that conveys data representing a third loudness normalization level, a third dynamic range adjustment level and third encoded audio information representing the audio information in an encoded form, wherein:
if a difference between the first and second loudness normalization levels does not exceed a threshold, the third loudness level represents the first loudness normalization level, the third dynamic range adjustment level represents the first dynamic range adjustment level and the third encoded audio information represents the first encoded audio information, and
if the difference between the first and second loudness normalization levels exceeds the threshold, the third loudness level is derived from the second loudness normalization level and the third dynamic range adjustment level is obtained in response to the audio information amplitude, the third loudness normalization level and the estimate of the compression profile.
8. The apparatus of claim 6 wherein, if the difference between the first and second loudness normalization levels exceeds the threshold, the third encoded audio information is generated by encoding the decoded audio information according to psychoacoustic principles.
9. The apparatus of claim 6 wherein, if the difference between the first and second loudness normalization levels exceeds the threshold, the third encoded audio information represents the first encoded audio information.
10. The apparatus of claim 6 wherein the input signal conveys a first number of bits representing the first dynamic range adjustment level and the output signal is generated with data rearranged to accommodate a second number of bits representing the third dynamic range adjustment level, wherein the first number of bits is greater than the second number of bits.
11. The apparatus of claim 6 wherein the input signal conveys a first number of bits representing the first dynamic range adjustment level and the output signal is generated with data rearranged to accommodate a second number of bits representing the third dynamic range adjustment level, wherein the first number of bits is less than the second number of bits.
12. The medium of claim 7 wherein, if the difference between the first and second loudness normalization levels exceeds the threshold, the third encoded audio information is generated by encoding the decoded audio information according to psychoacoustic principles.
13. The medium of claim 7 wherein, if the difference between the first and second loudness normalization levels exceeds the threshold, the third encoded audio information represents the first encoded audio information.
14. The medium of claim 7 wherein the input signal conveys a first number of bits representing the first dynamic range adjustment level and the output signal is generated with data rearranged to accommodate a second number of bits representing the third dynamic range adjustment level, wherein the first number of bits is greater than the second number of bits.
15. The medium of claim 7 wherein the input signal conveys a first number of bits representing the first dynamic range adjustment level and the output signal is generated with data rearranged to accommodate a second number of bits representing the third dynamic range adjustment level, wherein the first number of bits is less than the second number of bits.