TAS3103DBT datasheet(91/146 Pages) TI

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3−31

3.7.1

DRC Implementation

Figure 3−21 shows the three elements comprising the DRC: (1) an rms estimator, (2) a compression/expansion

coefficient computation engine, and (3) an attack/decay controller.

•

RMS estimator—This DRC element derives an estimate of the rms value of the audio data stream into the

DRC. For the DRC block shared by CH1 and CH2, two estimates are computed—an estimate of the CH1

audio data stream into the DRC, and an estimate of the CH2 audio data stream into the DRC. The outputs

of the two estimators are then compared, sample-by-sample, and the larger valued sample is forwarded

to the compression/expansion coefficient computation engine.

Two programmable parameters, ae and (1 – ae), set the effective time window over which the rms estimate

is made. For the DRC block shared by CH1 and CH2, the programmable parameters apply to both rms

estimators. The time window over which the rms estimation is computed can be determined by:

window +

* 1

n(1

* ae)

•

Compression/expansion coefficient computation—This DRC element converts the output of the rms

estimator to a logarithmic number, determines the region that the input resides, and then computes and

outputs the appropriate coefficient to the attack/decay element. Seven programmable parameters—T1, T2,

O1, O2, k0, k1, and k2—define the three compression/expansion regions implemented by this element.

•

Attack/decay control—This DRC element controls the transition time of changes in the coefficient computed

in the compression/expansion coefficient computation element. Four programmable parameters define the

operation of this element. Parameters ad and 1 − ad set the decay or release time constant to be used for

volume boost (expansion). Parameters aa and 1 − aa set the attack time constant to be used for volume

cuts. The transition time constants can be determined by:

ta +

* 1

n(1

* aa)

d +

* 1

n(1

* ad)

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