STA323W datasheet(32/41 Pages) STMICROELECTRONICS

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Table 33. Mix/Bass Management Block Diagram

After a mix is achieved, STA323W 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 STA323W 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.

C1MX1

C1MX2

C2MX1

C2MX2

C3MX1

C3MX2

High-Pass

Filter

High-Pass

Filter

Low-Pass

Filter

User-defined Mix Coefficients

Crossover Frequency determined

by XO setting.

User-defined when XO = 000

Channel #1

from EQ

Channel #2

from EQ

Channel#1

to GC/Vol

Channel#2

to GC/Vol

Channel#3

to GC/Vol

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