Adaptive gain control for digital audio samples in a media stream

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;

transmitting the first group of gain-adjusted digital audio samples to a remotely-located media player to generate sound based on the first group of gain-adjusted digital audio samples;

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, wherein the second set of digital audio samples follow the first set of digital audio samples, and wherein the second group of gain-adjusted digital audio samples follow the first group of gain-adjusted digital audio samples; and

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

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

L

k

=

∑

i

=

1

i

=

N

⁢



a

i



,

where a i represents the digital audio samples, and where the current block of digital audio samples includes N digital audio samples;

calculating a reference gain value (g r ) for the current block of digital audio samples in accordance with the expression

g

r

=

L

ref

L

k

,

where L ref is a reference loudness value;

calculating a maximum gain value (g m ) for the current block of digital audio samples in accordance with the expression

g

m

=

2

n

-

1

a

max

,

where n is the number of bits per digital audio sample, and where a max , is the maximum absolute sample value in the current block of digital audio samples;

calculating an estimated gain value (g e ) for the current block of digital audio samples in accordance with the expression g e =min(g r ,g m ); and

calculating a gain value for the current block of digital audio samples in accordance with the expression g k =min(w 1 g k-1 +w 2 g e , , g m ), wherein w 1 and W 2 are weighting factors, the values of w 1 and W 2 are variable for the fast gain adaptation scheme, and the values of w 1 and W 2 are fixed for the steady state gain adaptation scheme.

11. The method of claim 10 , wherein;

w 1 and w 2 are weighting factors;

w 1 +w 2 =1.0;

w 1 >0.0; and

w 2 >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 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, wherein the second block of digital audio samples follow the first block of digital audio samples, and wherein the second block of gain-adjusted digital audio samples follow the first block of gain-adjusted digital audio samples; and

means for transmitting gain-adjusted digital audio samples to a remotely-located media player, wherein the means for transmitting transmits the first block of gain-adjusted digital audio samples to the remotely-located media player to generate sound based on the first block of gain-adjusted digital audio samples, and thereafter transmits the second block of gain-adjusted digital audio samples to the remotely-located media player to generate sound based on the second block of gain-adjusted digital audio samples.

14. The system of claim 13 , 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.