TAS5504_06 datasheet(35/96 Pages) TI

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Introduction

SLES123 − October 2004

TAS5504

1.10.2.3 Slope Parameter Computation

In developing the equations used to determine the subaddress of the 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 + 1n–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 + 1n–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

1:2Expansion 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 + 1n *1 å n + –

3 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.

1.11 Output Mixer

The TAS5504 provides an 4x2 output mixer for channels 1 and 2. For channels 3 and 4, the TAS5504 provides

an 4x3 output mixer. These mixers allow each output to be any ratio of any two (three) signal processed

channels. The control parameters for the output crossbar mixer are programmable via the I2C interface.

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