STA382BWSTR datasheet(144/172 Pages) STMICROELECTRONICS

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STA382BWS

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Sub-band decomposition

The sub-band decomposition for B2DRC can be configured specifying the cutoff frequency.

The cutoff frequency can be programmed in two ways, using the XO bits in register 0x0C, or

using the “user programmable” mode (coefficients stored in RAM addresses 0x28 to 0x31).

For the user-programmable mode, use the formulas below to compute the high-pass filters:

where alpha = (1-sin(

ω0))/cos(ω0), and ω0 is the cutoff frequency.

A first-order filter is suggested to guarantee that for every

ω0 the corresponding low-pass

filter obtained as difference (as shown in Figure 24) will have a symmetric (relative to the HP

filter) frequency response, and the corresponding recombination after the DRC has low

ripple. Second-order filters can be used as well, but in this case the filter shape must be

carefully chosen to provide good low-pass response and minimum ripple recombination. For

second-order filters, it is not possible to give a closed formula to get the best coefficients, but

empirical adjustment should be done.

DRC settings

The DRC blocks used by B2DRC are the same as those described in Chapter 7.11. B2DRC

configure automatically the DRC blocks in anticlipping mode. Attack and release thresholds

can be selected using registers 0x32, 0x33, 0x34, 0x35, while attack and release rates are

configured by registers 0x12 and 0x14.

Band downmixing

The low-frequency band is down-mixed to the left and right channels at the B2DRC output.

Channel volume can be used to weight the bands recombination to fine-tune the overall

frequency response.

7.16.2

Extended post-scale range

Table 156.

Extended post-scale range

Post-scale is an attenuation by default. When PS48DB is set to 1, a 48-dB offset is applied

to the coefficient RAM value, so post-scale can act as a gain too.

b0 = (1 + alpha) / 2

a0 = 1

b1 = -(1 + alpha) / 2

a1 = -alpha

b2 = 0

a2 = 0

PS48DB

Mode

Post-scale value is applied as defined in coefficient RAM

Post-scale value is applied with +48 dB offset with respect to the

coefficient RAM value

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