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

• US 7,072,477 B1
• Filed: 07/09/2002
• Issued: 07/04/2006
• Est. Priority Date: 07/09/2002
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Kincaid, William S.
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Sked, Matthew J.
• Application Number:
  US10/192,231
• Time in Patent Office: 1,456 Days
• Field of Search: None
• US Class Current: 381/107
• CPC Class Codes: G06Q 99/00 Subject matter not provided for in other groups of this subclass
• CPC Class Codes: H03G 3/3089 Control of digital or coded signals
• CPC Class Codes: H03G 5/005 of digital signals
• CPC Class Codes: H04H 20/95 characterised by a specific format, e.g. an encoded audio stream

Abstract

Automatically normalizing a perceived loudness for a digitally encoded audio track formed of a number of channels during playback on a multimedia asset player is described. A number of auditory selectivity frequency bands are selected and for each channel in the track, a power value for each of the number of selectivity frequency bands is computed. Each of the power values is weighted by a sensitivity weighting factor and a sum value of all the weighted power values is then calculated. For the track, a perceived acoustic power value is calculated based upon the sum value for each of the channels and a normalization gain factor based upon the perceived acoustic power is calculated and associated with the track. During playback, the normalization gain factor is applied to the track.

Claims

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.