ADAPTIVE GAIN CONTROL FOR DIGITAL AUDIO SAMPLES IN A MEDIA STREAM

• US 20110019839A1
• Filed: 07/23/2009
• Published: 01/27/2011
• Est. Priority Date: 07/23/2009
• Status: Active Grant

• Current Assignee: Dish Network Technologies India Private Limited (Echostar Corporation)
• Original Assignee: Sling Media Pvt Ltd. (Echostar Corporation)
• Inventors: Nandury, Venkata Kishore
• Granted Patent: US 8,406,431 B2
• Time in Patent Office: Days
• US Class Current: 381/107
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• CPC Class Codes: H03G 7/007 of digital or coded signals
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones
• CPC Class Codes: H04S 2400/13 Aspects of volume control, not necessarily automatic, in stereophonic sound systems

Abstract

An adaptive gain control system and related operating method for digital audio samples is provided. The method is suitable for use with a digital media encoding system that transmits encoded media streams to a remotely-located presentation device such as a media player. The method begins by initializing the processing of a media stream. Then, the method adjusts the gain of a first set of digital audio samples in the media stream using a fast gain adaptation scheme, resulting in a first group of gain-adjusted digital audio samples having normalized volume during presentation. The method continues by adjusting the gain of a second set of digital audio samples in the media stream using a steady state gain adaptation scheme that is different than the fast gain adaptation scheme, resulting in a second group of gain-adjusted digital audio samples having normalized volume during presentation.

Claims

1. An adaptive gain control method for digital audio samples, the method comprising:

initializing processing of a media stream;

adjusting gain of a first set of digital audio samples in the media stream using a fast gain adaptation scheme, resulting in a first group of gain-adjusted digital audio samples having normalized volume during presentation; and

thereafter, adjusting gain of a second set of digital audio samples in the media stream using a steady state gain adaptation scheme that is different than the fast gain adaptation scheme, resulting in a second group of gain-adjusted digital audio samples having normalized volume during presentation.

2. The method of claim 1, wherein adjusting gain of the first set of digital audio samples is performed for a predetermined time period after initializing processing of the media stream.

3. The method of claim 1, wherein adjusting gain of the first set of digital audio samples is performed for a predetermined number of blocks of digital audio samples after initializing processing of the media stream.

4. The method of claim 3, wherein:

one digital audio sample is represented by sixteen bits; and

one block of digital audio samples is represented by 1024 digital audio samples.

5. The method of claim 1, further comprising, after adjusting gain of the second set of digital audio samples:

initializing processing of a second media stream;

adjusting gain of a third set of digital audio samples in the second media stream using the fast gain adaptation scheme, resulting in a third group of gain-adjusted digital audio samples having normalized presentation volume; and

thereafter, adjusting gain of a fourth set of digital audio samples in the second media stream using the steady state gain adaptation scheme, resulting in a fourth group of gain-adjusted digital audio samples having normalized presentation volume.

6. The method of claim 1, further comprising:

calculating a loudness estimate for a block of digital audio samples in the media stream;

comparing the loudness estimate to a silence threshold value; and

applying a multiplicative gain of one to the block of digital audio samples when the loudness estimate is less than the silence threshold value.

7. The method of claim 1, further comprising the step of calculating a gain value for a current block of digital audio samples in the media stream, wherein the gain value is influenced by a previous gain value for a previous block of digital audio samples in the media stream.

8. The method of claim 1, further comprising:

calculating a loudness estimate for a block of digital audio samples in the media stream;

determining a reference gain value based upon the loudness estimate and a reference loudness value; and

calculating a gain value for the block of digital audio samples, wherein the gain value is influenced by the reference gain value.

9. The method of claim 1, further comprising:

calculating a maximum gain value for a block of digital audio samples in the media stream; and

calculating a gain value for the block of digital audio samples, wherein the gain value is influenced by the maximum gain value.

10. The method of claim 1, wherein adjusting gain of the first set of digital audio samples and adjusting gain of the second set of digital audio samples each comprises:

obtaining a current block of digital audio samples in the media stream for processing;

calculating a loudness estimate (L_k) for the current block of digital audio samples in accordance with the expression

11. The method of claim 10, wherein;

w₁ and w₂ are weighting factors;

w₁+w₂=1.0;

w₁>

0.0; and

w₂>

0.0.

12. The method of claim 1, further comprising:

transmitting the first group of gain-adjusted digital audio samples to a remotely-located digital media player; and

transmitting the second group of gain-adjusted digital audio samples to the remotely-located digital media player.

13. A computer program product, tangibly embodied in a computer-readable medium, the computer program product being operable to cause a digital media processing device to perform operations for a media stream, comprising:

calculating a loudness estimate for a current block of digital audio samples in the media stream;

calculating a reference gain value for the current block of digital audio samples, the reference gain value being influenced by the loudness estimate;

calculating a maximum gain value for the current block of digital audio samples;

calculating an estimated gain value for the current block of digital audio samples, the estimated gain value being influenced by the reference gain value and the maximum gain value;

calculating a gain value for the current block of digital audio samples, the gain value being influenced by the estimated gain value, the maximum gain value, and a previous gain value for a previous block of digital audio samples in the media stream; and

modifying the current block of digital audio samples by applying the gain value to the digital audio samples in the current block of digital audio samples.

14. The computer program product of claim 13, wherein the computer program product is operable to cause the digital media processing device to perform further operations, comprising:

comparing the loudness estimate to a silence threshold value; and

applying a multiplicative gain value of one to the current block of digital audio samples when the loudness estimate is less than the silence threshold value.

15. The computer program product of claim 13, wherein calculating the loudness estimate is performed in accordance with the expression

16. The computer program product of claim 15, wherein calculating the reference gain value is performed in accordance with the expression

17. The computer program product of claim 16, wherein:

calculating the maximum gain value is performed in accordance with the expression

18. The computer program product of claim 17, wherein calculating the gain value is performed in accordance with the expression g_k=min(w₁g_k-1+w₂g_e, g_m), where g_k is the gain value, and w₁ and w₂ are weighting factors.

19. A system for processing digital audio samples in a media stream, the system comprising:

a first means for adjusting gain of a first block of digital audio samples in the media stream using a fast gain adaptation scheme, resulting in a first block of gain-adjusted digital audio samples;

a second means for adjusting gain of a second block of digital audio samples in the media stream using a steady state gain adaptation scheme that is different than the fast gain adaptation scheme, resulting in a second block of gain-adjusted digital audio samples; and

means for transmitting gain-adjusted digital audio samples to a remotely-located media player.

20. The system of claim 19, wherein each of the first means for adjusting and the second means for adjusting is configured to:

calculate a loudness estimate for a current block of digital audio samples in the media stream;

calculate a reference gain value for the current block of digital audio samples, the reference gain value being influenced by the loudness estimate;

calculate a maximum gain value for the current block of digital audio samples;

calculate an estimated gain value for the current block of digital audio samples, the estimated gain value being influenced by the reference gain value and the maximum gain value;

calculate a gain value for the current block of digital audio samples, the gain value being influenced by the estimated gain value, the maximum gain value, and a previous gain value for a previous block of digital audio samples in the media stream; and

modify the current block of digital audio samples by applying the gain value to the digital audio samples in the current block of digital audio samples.