Datasheet

3−30
Commands to reconfigure the reverb delay and delay lines should not be issued as stand-alone 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: No error flags are 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)
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.
Two distinct DRC blocks are in the TAS3103A. 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 3−21 shows the positioning of the DRC block in the TAS3103A 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 TAS3103A 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
Σ
Soft
Volume
Loudness
Σ Σ
DRC Bypass
DRC
DRC
Input Mixer
DRC
Input Mixer
Σ
CH1/CH2 DRC Only
Figure 3−21. DRC Positioning in TAS3103A Processing Flow