TAS3103DBT datasheet(89/146 Pages) TI

89 / 146 page

3−29

Commands to reconfigure the reverb delay and delay lines should not be issued as standalone commands. When

new delay assignments are issued, the content of the 4K memory resource used to implement the delay lines is not

flushed. It takes a finite time for the memory to refill with samples in correspondence with its new assignments, and

until this time has elapsed, audio samples can be output on the wrong channel. For this reason, it is recommended

that all delay line assignment commands be preceded by a mute command, and followed by an unmute command.

CAUTION: There are no error flags issued if the delay line assignments exceed the

capacity of the 4K memory resource, but undefined and erratic behavior results if the

delay line capacity is exceeded.

3.7

Dynamic Range Control (DRC)

The DRC provides both compression and expansion capabilities over three separate and definable regions of audio

signal levels. Programmable threshold levels set the boundaries of the three regions. Within each of the three regions

a distinct compression or expansion transfer function can be established and the slope of each transfer function is

determined by programmable parameters. The offset (boost or cut) at the two boundaries defining the three regions

can also be set by programmable offset coefficients. The DRC implements the composite transfer function by

computing a 5.23 format gain coefficient from each sample output from the rms estimator. This gain coefficient is then

applied to a mixer element, whose other input is the audio data stream. The mixer output is the DRC-adjusted audio

data.

There are two distinct DRC blocks in the TAS3103. One DRC services two monaural channels—CH1 and CH2. This

DRC computes rms estimates of the audio data streams on both CH1 and CH2. The two estimates are then compared

on a sample-by-sample basis, and the larger of the two is used to compute the compression/expansion gain

coefficient. The gain coefficient is then applied to both CH1 and CH2 audio. The other DRC services only monaural

channel CH3. This DRC also computes an rms estimate of the signal level on CH3, and this estimate is used to

compute the compression/expansion gain coefficient applied to CH3 audio.

Figure 3−19 shows the positioning of the DRC block in the TAS3103 processing flow. As seen, the DRC input can

come from either before or after soft volume control and loudness processing, or can be a weighted combination of

both. The mixers feeding the DRC control the selection of which audio data stream or combination thereof, is input

into the DRC. The mixers also provide a means of gaining or attenuating the signal level into the DRC. If the DRC

setup is referenced to the 0-dB level at the TAS3103 input, the coefficient values for these mixers must be taken into

account. Discussions and examples that follow further explore the role the mixers play in setting up the transfer

function of the DRC.

Channel

BiQuad

Filter Bank

DRC-Derived

Gain Coefficient

From

Effects

Block

Base

and

Treble

Base and Treble

Bypass

Soft

Volume

Loudness

DRC Bypass

DRC

Input Mixer

DRC

Input Mixer

CH 1/2 DRC Only

Figure 3−19. DRC Positioning in TAS3103 Processing Flow

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