DAC
2.4.4.2.4 DRC Attack Rate
When the output of the DAC Digital Volume Control exceeds the programmed DRC Threshold, the gain
applied in the DAC Digital Volume Control is progressively reduced to avoid the signal from saturating the
channel. This process of reducing the applied gain is called Attack. To avoid audible artifacts, the gain is
reduced slowly with a rate equaling the Attack Rate programmable via Page 0, Register 70, Bits D7-D4).
Attack Rates can be programmed from 4dB gain change per 1/DAC_FS to 1.2207e-5dB gain change per
1/DAC_FS.
Attack Rates should be programmed such that before the output of the DAC Digital Volume control can
clip, the input signal should be sufficiently attenuated. High Attack Rates can cause audible artifacts, and
too-slow Attack Rates may not be able to prevent the input signal from clipping.
The recommended DRC Attack Rate value is 1.9531e-4 dB per 1/DAC_FS.
2.4.4.2.5 DRC Decay Rate
When the DRC detects a reduction in output signal swing beyond the programmed DRC Threshold, the
DRC enters a Decay state, where the applied gain in Digital Volume Control is gradually increased to
programmed values. To avoid audible artifacts, the gain is slowly increased with a rate equal to the Decay
Rate programmed through Page 0, Register 70, Bits D3-D0). The Decay Rates can be programmed from
1.5625e-3dB per 1/DAC_FS to 4.7683e-7dB per 1/DAC_FS. If the Decay Rates are programmed too high,
then sudden gain changes can cause audible artifacts. However, if it is programmed too slow, then the
output may be perceived as too low for a long time after the peak signal has passed.
The recommended Value of DRC Decay Rate is 2.4414e-5 dB per 1/DAC_FS.
2.4.4.2.6 Example Setup for DRC
•
PGA Gain = 12 dB
•
Threshold = -24 dB
•
Hysteresis = 3 dB
•
Hold time = 0 ms
•
Attack Rate = 1.9531e-4 dB per 1/DAC_FS
•
Decay Rate = 2.4414e-5 dB per 1/DAC_FS
Script
w 30 00 00
#Go to Page 0
w 30 41 18
#DAC => 12 db gain left
w 30 42 18
#DAC => 12 db gain right
w 30 44 7F
#DAC => DRC Enabled for both channels, Threshold = -24 db, Hysteresis = 3 dB
w 30 45 00
#DRC Hold = 0 ms, Rate of Changes of Gain = 0.5 dB/Fs'
w 30 46 B6
#Attack Rate = 1.9531e-4 dB/Frame , DRC Decay Rate =2.4414e-5 dB/Frame
w 30 00 2E
#Go to Page 46
w 30 34 7F AB 00 00 80 55 00 00 7F 56 00 00
#DRC HPF
w 30 40 00 11 00 00 00 11 00 00 7F DE 00 00
#DRC LPF
46
TLV320DAC3203 Application
SLAU434 – May 2012
Copyright © 2012, Texas Instruments Incorporated