STA326
Table 33. Mix/Bass Management Block Diagram
Channel #1
from EQ
C1MX1
High-Pass
XO
Filter
Channel#1
to GC/Vol
+
Channel #2
from EQ
C1MX2
C2MX1
+
High-Pass
XO
Filter
Channel#2
to GC/Vol
C2MX2
C3MX1
+
Low-Pass
XO
Filter
Channel#3
to GC/Vol
C3MX2
User-defined Mix Coefficients Crossover Frequency determined
by XO setting.
User-defined when XO = 000
After a mix is achieved, STA326 also provides the capability to implement crossver filters on all channels
corresponding to 2.1 bass management solution. Channels 1-2 use a 1st order high-pass filter and chan-
nel 3 uses a 2nd order low-pass filter corresponding to the setting of the XO bits of I2C register 0Ch. If XO
= 000, user specified crossover filters are used.
By default these coefficients correspond to pass-through. However, the user can write these coefficients
in a similar way as the EQ biquads. When user-defined setting is selected, the user can only write 2nd
order crossover filters. This output is then passed on to the Volume/Limiter block.
8.5 Calculating 24-Bit Signed Fractional Numbers from a dB Value
The pre-scale, mixing, and post-scale functions of the STA326 use 24-bit signed fractional multipliers to
attenuate signals. These attenuations can also invert the phase and therefore range in value from -1 to
+1. It is possible to calculate the coefficient to utilize for a given negative dB value (attenuation) via the
equations below.
– Non-Inverting Phase Numbers 0 to +1 :
– Coefficient = Round(8388607 * 10^(dB/20))
– Inverting Phase Numbers 0 to -1 :
– Coefficient = 16777216 - Round(8388607 * 10^(dB/20))
As can be seen by the preceding equations, the value for positive phase 0dB is 0x7FFFFF and the value
for negative phase 0dB is 0x800000.
32/43
STMICROELECTRONICS [ ST ]
