TAS5518 datasheet(33/103 Pages) TI

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Introduction

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 1−7 in the 8-channel mode and

channels 1−4, 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 1−8

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 1−8. DRC Recommended Changes From TAS5518 Defaults

I2C

SUBADDRESS

RECOMMENDED TIME

CONSTANT (MS)

RECOMMENDED

HEX VALUE

DEFAULT HEX

0x98

DRC1 energy

0000883F

DRC1 (1 – energy)

007F77C0

0x9C

DRC1 attack

0000883F

DRC1 (1 – attack)

007F77C0

DRC1 decay

0001538F

000000AE

DRC1 (1 – decay)

007EAC70

007FFF51

0x9D

DRC2 energy

0000883F

DRC2 (1 – energy)

007F77C0

0xA1

DRC2 attack

0000883F

DRC2 (1 – attack)

007F77C0

DRC2 decay

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

Table 1−8.

•

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 1−19 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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