TAS3103ADBT datasheet(98/154 Pages) TI2

98 / 154 page

3−35

INPUT +

DESIRED )

24.0824 dB

6.0206

Gains or boosts are represented as negative numbers; cuts or attenuation are represented as positive numbers. For

example, to achieve a boost of 21 dB at threshold T1, the I2C coefficient value entered for O1 must be:

INPUT +

–21 dB

) 24.0824 dB

6.0206

+ 0.51197555

+ 0.1000_0011_0001_1101_0100

+ 0x00000041886A in 25.23 format

More examples of offset computations follow.

3.7.2.3 Slope Parameter Computation

In developing the equations used to determine the subaddress input value required to realize a given compression

or expansion within a given region of the DRC, the following convention is adopted.

DRC Transfer = Input Increase : Output Increase

If the DRC realizes an output increase of n dB for every dB increase in the rms value of the audio into the DRC, a

1:n expansion is being performed. If the DRC realizes a 1-dB increase in output level for every n-dB increase in the

rms value of the audio into the DRC, a n:1 compression is being performed.

For 1:n expansion, the slope k can be found by:

k = n − 1

For n:1 compression, the slope k can be found by: k

+ 1

n –1

In both expansion (1:n) and compression (n:1), n is implied to be greater than 1. Thus, for expansion:

k = n −1 means k > 0 for n > 1. Likewise, for compression, k

+ 1

n –1 means −1 < k < 0 for n > 1. Thus, it appears that

k must always lie in the range k > −1.

The DRC imposes no such restriction, and k can be programmed to values as negative as −15.999. To determine

what results when such values of k are entered, it is first helpful to note that the compression and expansion equations

for k are actually the same equation. For example, a 1:2 expansion is also a 0.5:1 compression.

0.5 Compression

å k + 1

0.5

–1

+ 1

1 : 2 Expansion

å k + 2–1 + 1

As can be seen, the same value for k is obtained either way. The ability to choose values of k less than −1 allows the

DRC to implement negative-slope transfer curves within a given region. Negative-slope transfer curves are usually

not associated with compression and expansion operations, but the definition of these operations can be expanded

to include negative-slope transfer functions. For example, if k = −4

Compression equation: k

+*4 + 1

n *1 å n +*

å*0.3333 : 1 compression

Expansion equation: k

+*4 + n * 1 å n +*3 å 1: *3 expansion

With k = −4, the output decreases 3 dB for every 1-dB increase in the rms value of the audio into the DRC. As the

input increases in volume, the output decreases in volume.

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