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| 型号： | TAS5518PAGR |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 消费家电 |
| 英文描述： | SPECIALTY CONSUMER CIRCUIT, PQFP64 |
| 封装： | GREEN, PLASTIC, TQFP-64 |
| 文件页数： | 32/105页 |
| 文件大小： | 1514K |
| 代理商： | TAS5518PAGR |
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Introduction
24
SLES115 — August 2004
TAS5518
1.11 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 TAS5518. DRC1 services channels 17 in the 8-channel mode and
channels 14, and 7 in the 6-channel mode. This DRC computes rms estimates of the audio data streams on
all channels that it controls. The estimates are then compared on a sample-by-sample basis and the larger
of the estimates is used to compute the compression/expansion gain coefficient. The gain coefficient is then
applied to appropriate channels audio stream. DRC2 services only channel 8. This DRC also computes an
rms estimate of the signal level on channel 8 and this estimate is used to compute the compression/expansion
gain coefficient applied to the channel 8 audio stream.
All of the TAS5518 default values for DRC can be used except for the DRC1 decay and DRC2 decay. Table 18
shows the recommended time constants and their HEX values. If the user wants to implement other DRC
functions, Texas Instruments recommends using the automatic loudspeaker equalization (ALE) tool available
from Texas Instruments. The ALE tool allows the user to select the DRC transfer function graphically. It will
then output the TAS5518 hex coefficients for download to the TAS5518.
Table 18. DRC Recommended Changes From TAS5518 Defaults
I2C
SUBADDRESS
REGISTER FIELDS
RECOMMENDED TIME
CONSTANT (MS)
RECOMMENDED
HEX VALUE
DEFAULT HEX
0x98
DRC1 energy
5
0000883F
DRC1 (1 – energy)
007F77C0
0x9C
DRC1 attack
5
0000883F
DRC1 (1 – attack)
007F77C0
DRC1 decay
2
0001538F
000000AE
DRC1 (1 – decay)
007EAC70
007FFF51
0x9D
DRC2 energy
5
0000883F
DRC2 (1 – energy)
007F77C0
0xA1
DRC2 attack
5
0000883F
DRC2 (1 – attack)
007F77C0
DRC2 decay
2
0001538F
000000AE
DRC2 (1 – decay)
007EAC70
007FFF51
Recommended DRC set-up flow if the defaults are used:
After power up, load the recommended hex value for DRC1 and DRC2 decay and (1 – decay). See
Enable either the pre-volume or post-volume DRC
Recommended DRC set-up flow if the DRC design uses values different from the defaults:
After power up, load all DRC coefficients per the DRC design.
Enable either the pre-volume or post-volume DRC
Figure 119 shows the positioning of the DRC block in the TAS5518 processing flow. As seen, the DRC input
can come from either before or after soft volume control and loudness processing.
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