TAS5705
www.ti.com ...................................................................................................................................................................................................... SLOS549–JUNE 2008
Dynamic Range Control (DRC)
The DRC input/output diagram is shown in Figure 42.
k
1:1 Transfer Function
Implemented Transfer Function
T
DRC Input Level
M0091-01
Figure 42. Dynamic Range Control
The TAS5705 has single-threshold dynamic range compressors (one for all satellites and one for the subwoofer).
There are two distinct DRC blocks. DRC1 controls the satellite channels. DRC2 controls the subwoofer channel.
The DRC provides compression capabilities above the threshold region of audio signal levels. A programmable
threshold level sets the boundaries of the two regions. The offset (boost or cut) can be defined by a
programmable offset coefficient. The DRC implements the composite transfer function by computing a
3.23-format gain coefficient from each sample output of an RMS estimator. This gain coefficient is then applied to
a mixer element, whose other input is the audio data channel. The mixer output is the DRC-adjusted audio data.
The audio is the signal level following the volume control, as specified by the user. The estimates are then
compared on a sample-by-sample basis, and the largest is used to compute the compression gain coefficient.
The gain coefficient is then applied to the audio of the satellite group.
The control parameters for the dynamic range controls are programmable via the I2C interface.
The DRC control for each channel is performed by two control bits. The encoding is shown in Table 2.
Table 2. DRC Control Inputs
0x46 Bit 1
0x46 Bit 0
Description
Disable DRC1
Enable DRC1
Disable DRC2
Enable DRC2
X
X
0
1
0
1
X
X
The DRC scheme has a single threshold, offset, and slope (all programmable). There is one ganged DRC for the
left/right channels and one DRC for the subwoofer channel.
•
•
•
Thresholds T1 and T2 define the thresholds for DRC1 and DRC2, respectively.
Offsets O1 and O2 define the gain coefficients for DRC1 and DRC2, respectively.
The magnitudes of slopes k1 and k2 define the degree of compression to be performed above the threshold
for DRC1 and DRC2, respectively.
The three sets of parameters are all defined in logarithmic space, and adhere to the following rules.
•
The maximum input sample into the DRC is referenced at 0 dB. All values below this maximum value then
have negative values in logarithmic (dB) space.
•
Thresholds T1 and T2 define, in dB, the boundaries of the regions of the DRC, as referenced to the RMS
value of the data into the DRC. 0-dB threshold settings reference the maximum-valued RMS input into the
DRC, and negative-valued thresholds reference all other RMS input levels. Positive-valued thresholds have
no physical meaning and are not allowed. In addition, zero-valued threshold settings are not allowed.
Copyright © 2008, Texas Instruments Incorporated
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