STA3398 datasheet(66/77 Pages) STMICROELECTRONICS

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STA339BW

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Doc ID 15251 Rev 5

6.18.1

Dual-band DRC

The STA339BW provides a dual-band DRC (B2DRC) on the left- and right-channel data

path, as depicted in Figure 20. Dual-band DRC is activated by setting MDRC[1:0] = 1x.

Figure 20.

B2DRC scheme

The low-frequency information (LFE) is extracted from the left and right channels by

removing the high frequencies with a programmable Biquad filter, so that, using the original

signal, the difference signal can be computed. Limiter 1 (DRC1) is then used to control the

left and right high-frequency component amplitudes while limiter 2 (DRC2) is used to control

the low-frequency components (see Chapter 6.11).

The cutoff frequency of the high-pass filters can be user defined, XO[3:0] = 0, or selected

from the pre-defined values.

DRC1 and DRC2 are then used to independently limit the left- and right-channel high

frequencies and the LFE-channel amplitude (see Chapter 6.11) as well as their volume

control. Note that, in this configuration, the dedicated channel-3 volume control can actually

be used as a bass boost enhancer as well (0.5 dB/step resolution).

The processed LFE channel is then recombined with the L and R channels in order to

reconstruct the 2.0 output signal.

Sub band decomposition

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

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

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

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

where alpha = (1-sin(

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

b0 = (1 + alpha) / 2

a0 = 1

b1 = -(1 + alpha) / 2

a1 = -alpha

b2 = 0

a2 = 0

Pass

Filter

Pass

Filter

B2DRC

Hi-pass

filter

B2DRC

Hi-pass

filter

Ch1

Volume

Vol

And

Limiter

DRC1

Ch2

Volume

DRC1

Ch3

Volume

Vol

And

Limiter

DRC2

Ch3

Volume

Vol

And

Limiter

DRC2

Pass

Filter

Pass

Filter

B2DRC

Hi-pass

filter

B2DRC

Hi-pass

filter

Ch1

Volume

Vol

And

Limiter

DRC1

Ch2

Volume

DRC1

Ch3

Volume

Vol

And

Limiter

DRC2

Ch3

Volume

Vol

And

Limiter

DRC2

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