Device overview STA380BW
The band splitter filter coefficients have a user-selectable range [-1, 1), [-2, 2) and [-4, 4).
The RAM coefficient 0x7 is responsible for these settings according to Table 8 . The range
default value is [-4, 4).
Table 8. Coefficients extended-range configuration 0x74h
CEXT_Bx[1] CEXT_Bx[0] Range
1
1
0
0
0
1
0
1
[-1;1)
[-2;2)
[-4;4)
Reserved
Please refer to
Section 6.23: User-defined coefficient control registers (addr 0x27 - 0x37)
and to
Table 12 for further details.
Figure 11. Band splitter with 4 th order filtering
BQ 0
Band Splitter
BQ 1
Input
Ch x
Band 0
…
Output
Ch x
+ =
BQ 0 BQ 1
Band 1
…
The level meter block measures the input signal level (in dB). Two kinds of measures are performed: peak and RMS. The mapper configuration and the input signal automatically determine which measurement to take into account.
Obsolete Product(s) - Obsolete Product(s)
4.3.4 Mapper
The mapper block computes the appropriate attenuation value (expressed in dB) to be applied to the signal, basing its calculations on the level meter output value, on the compressor threshold and on the limiter threshold.The attenuation value is then passed to the attenuator block.
30/162 DocID024543 Rev 1
STA380BW Device overview
The STC reacts differently depending on these three parameters ( Figure 12 ):
level meter output value < compressor threshold < limiter threshold: under these circumstances the signal level is small enough to not require any type of limiting/compressing action. The signal remains unchanged.
compressor threshold < level meter output value < limiter threshold: under these circumstances the signal level is compressed to a ratio determined by the compressor rate.
compressor threshold < limiter threshold < level meter output value: under these circumstances the signal level exceeds the limiter threshold which represents the maximum output power allowed. The signal is limited to avoid unpredictable effects and damages.
The compressor threshold, the limiter threshold and the compressor rate are all userselectable parameters. The compressor threshold range of value is [-48, 0] dB with a
0.25 dB step. The limiter threshold range of values is [-24, +12] dB with a 0.25 dB step. The compressor ratio range of value is [0, 15], the meaning of these values is specified in
Table 9
. For further details please refer to Table 11 . Either setting the compressor rate to 1:1
or setting the compressor threshold greater than the limiter threshold makes the STC behave as a pure limiter (
Figure 13 ).
Figure 12. STCompressor
TM
behavior
Linear Zone
Compression Zone
Limiting Zone
L.T.
C.R.
C.T.
C.T.
L.T.
INPUT
L.T. comp
[dB]
Obsolete Product(s) - Obsolete Product(s)
DocID024543 Rev 1 31/162
Device overview
L.T.
Figure 13. STCompressor TM behavior as a limiter
Linear Zone
Limiting Zone
STA380BW
L.T.
INPUT
[dB]
Compressor ratio
Table 9. Compressor ratio
Ratio value
6
7
4
5
8
9
2
3
0
1
1:1
1:1.25
1:1.5
1:1.75
1:2
1:2.5
1:3
1:3.5
1:4
1:4.5
10
11
1:5
1:5.5
12 1.6
Obsolete Product(s) - Obsolete Product(s)
13 1:7
14
15
1:8
1:16
32/162 DocID024543 Rev 1
