Datasheet

O1
INPUT
+
–21 dB ) 24.0824 dB
6.0206
+ 0.51197555
+ 0.1000_0011_0001_1101_0100
+ 0x00000041886A in 25.23 format
k +
1
n
* 1
k +
1
n
* 1
0.5 : 1 compression å k +
1
0.5
* 1 + 1
1 : 2 expansion å k + 2 * 1 + 1
Compression equation: k + *4 +
1
n
*1 å n + *
1
3
å *0.3333 : 1 compression
Expansion equation: k + *4 + n * 1 å n + * 3 å 1 : *3 expansion
TAS5508C
SLES257–SEPTEMBER 2010 www.ti.com
2.10.2.3 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, an n : 1 compression is being performed.
k = n – 1
For n : 1 compression, the slope k can be found by:
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, 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.
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
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.
2.11 Output Mixer
The TAS5508C provides an 8×2 output mixer for channels 1, 2, 3, 4, 5, and 6. For channels 7 and 8, the
TAS5508C provides an 8×3 output mixer. These mixers allow each output to be any ratio of any two (or
three) signal-processed channels. The control parameters for the output crossbar mixer are programmable
via the I
2
C interface.
38 Description Copyright © 2010, Texas Instruments Incorporated
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