Method and apparatus for automatically normalizing a perceived volume level in a digitally encoded file

1. A method for automatically normalizing a perceived loudness for a digitally encoded audio track formed of a number of channels during playback on a multimedia asset player, comprising

selecting a number of auditory selectivity frequency bands;

computing a power value for each of the number of selectivity frequency bands for each channel in the audio track;

weighting each of the power values by a sensitivity weighting factor for each channel in the audio track;

calculating an average sum value of all the weighted power values for each channel in the audio track;

calculating a perceived acoustic power value based upon the average sum value for each of the channels by determining a maximum average sum value for all channels and dividing the maximum average sum for all channels by a power scale factor used to map the perceived acoustic power value to a predefined range for the audio track;

calculating a normalization gain factor based upon the perceived acoustic power for the audio track;

associating the normalization gain factor with the audio track; and

applying the normalization gain factor to the track during playback.

2. A method as recited in claim 1 wherein the predefimed range is approximately 0 to approximately 10,000.

3. A method as recited in claim 1 , wherein the calculating a normalization gain factor Gn comprises:

calculating an inverse value of the perceived acoustic power value; and

calculating a square root value of the inverse value.

4. A method as recited in claim 3 , further comprising;

calculating a scaled normalization gain factor by multiplying the normalization gain factor by a normalization scaling factor (NSF) wherein the normalization scale factor takes on a value such that the scaled normalization gain factor is substantially equal to 1.0 representative of a no change condition for an average track.

5. A method as recited in claim 4 , wherein a value of the NSF is in the range of approximately 0 to approximately 10000.

6. A method as recited in claim 4 , wherein the associating comprises:

incorporating the scaled normalization gain factor into a tag;

associating the tag with the track.

7. A method as recited in claim 4 wherein applying comprises:

multiplying each sample of the track by the associated scaled normalization gain factor.

8. A method as recited in claim 4 wherein applying comprises:

multiplying selected samples of the track by the associated scaled normalization gain factor.

9. A method as recited in claim 1 , wherein the digitally encoded audio track is an MP3 type audio track.

10. An apparatus for automatically normalizing a perceived loudness for a digitally encoded audio track formed of a number of channels during playback on a multimedia asset player, comprising:

means for selecting a number of auditory selectivity frequency bands;

means for computing a power value for each of the number of selectivity frequency bands for each channel in the audio track;

means for weighting each of the power values by a sensitivity weighting factor for each channel in the audio track;

means for calculating an average sum value of all the weighted power values for each channel in the audio track;

means for calculating a perceived acoustic power value based upon the average sum value for each of the channels by determining a maximum average sum value for all channels and dividing the maximum average sum for all channels by a power scale factor used to map the perceived acoustic power value to a predefined range for the audio track;

means for calculating a normalization gain factor based upon the perceived acoustic power for the audio track;

means for associating the normalization gain factor with the audio track; and

means for applying the normalization gain factor to the track during playback.

11. An apparatus as recited in claim 10 wherein the predefined range is approximately 0 to approximately 10,000.

12. An apparatus as recited in claim 10 , wherein the calculating a normalization gain factor Gn comprises:

means for calculating an inverse value of the perceived acoustic power value; and

means for calculating a square root value of the inverse value.

13. An apparatus as recited in claim 12 , further comprising:

means for calculating a scaled normalization gain factor by multiplying the normalization gain factor by a normalization scaling factor (NSF) wherein the normalization scale factor takes on a value such that the scaled normalization gain factor is substantially equal to 1.0 representative of a no change condition for an average track.

14. An apparatus as recited in claim 13 , wherein a value of the NSF is in the range of approximately 0 to approximately 10000.

15. An apparatus as recited in claim 13 , wherein the associating comprises:

means for incorporating the scaled normalization gain factor into a tag;

means for associating the tag with the track.

16. An apparatus as recited in claim 13 wherein applying comprises;

means for multiplying each sample of the track by the associated scaled normalization gain factor.

17. An apparatus as recited in claim 13 wherein applying comprises:

means for multiplying selected samples of the track by the associated scaled normalization gain factor.

18. An apparatus as recited in claim 10 , wherein the digitally encoded audio track is an MP3 type audio track.