STA350B datasheet(77/94 Pages) STMICROELECTRONICS

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STA350B, STA350BW

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 the difference (as shown in Figure 32) will have a symmetric (relative to 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 8.11. 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 down-mixing

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.

8.18.2

EQ DRC mode

Setting MDRC = 01, it is possible to add a programmable biquad (the XO biquad at RAM

addresses 0x28 to 0x2C is used for this purpose) to the Limiter/compressor measure path

(side chain). Using EQDRC the peak detector input can be shaped in frequency using the

programmable biquad. For example if a +2 dB bass boost is applied (using a low shelf filter

for example), the effect is that the EQDRC output will limit bass frequencies to -2 dB below

the selected attack threshold.

Generally speaking, if the biquad boosts frequency f with an amount of X dB, the level of a

compressed sine wave at the output will be TH - X, where TH is the selected attack

threshold.

Note:

EQDRC works only if the biquad frequency response magnitude is

≥ 0 dB for every

frequency.

b0 = (1 + alpha) / 2

a0 = 1

b1 = -(1 + alpha) / 2

a1 = -alpha

b2 = 0

a2 = 0

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