TAS5548 datasheet(25/120 Pages) TI

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f − Frequency − Hz

20k

100

G001

−10

−20

−40

−30

10k

TAS5548

www.ti.com

SLES270 – NOVEMBER 2012

Table 3-4. Example Loudness Function Parameters

LOUDNESS

DESCRIPTION

USAGE

DATA

I2C

EXAMPLE

TERM

FORMAT

SUB-

HEX

FLOAT

ADDRESS

H(Z)

Loudness biquad

Controls shape of

5.23

0x95

b0 = 0000 8ACE

b0 = 0.004236

loudness curves

b1 = 0000 0000

b1 = 0

b2 = FFFF 7532

b2 = –0.004236

a1 = FF01 1951

a1 = –1.991415

a2 = 007E E914

a2 = 0.991488

Loudness gain

Loudness function

5.23

0x91

FFC0 0000

–0.5

Loudness offset

Loudness function

9.23

0x92

0000 0000

Gain

Switch to enable

5.23

0x93

0080 0000

loudness (ON = 1, OFF = 0)

Offset

9.23

0x94

0000 0000

See Figure 3-14 for the resulting loudness function at different gains.

Figure 3-14. Loudness Example Plots

3.8

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.

The TAS5548 has two distinct DRC blocks. 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 the appropriate channel audio streams. 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.

TAS5548 DAP Architecture

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