TAS5548DCAR datasheet(37/116 Pages) TI1

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B0017-01

Loudness

Biquad

H(z)

Audio Out

Audio In

Loudness Function = f(V)

TAS5548

www.ti.com

SLES270A – NOVEMBER 2012 – REVISED APRIL 2015

Figure 34. Loudness Compensation Functional Block Diagram

Loudness function = f(V) = G × [2(Log V) × LG + LO] + O or alternatively,

Loudness function = f(V) = G × [VLG × 2LO] + O

For example, for the default values LG = –0.5, LO = 0, G = 1, and O = 0, then:

Loudness function = 1/SQRT(V), which is the recommended transfer function for loudness. So,

Audio out = (audio in) × V + H(Z) × SQRT(V). Other transfer functions are possible.

Table 9. Default Loudness Compensation Parameters

LOUDNESS

DESCRIPTION

USAGE

DATA

I2C

DEFAULT

FORMAT

TERM

SUB-

HEX

FLOAT

ADDRESS

Max volume

Gains audio

5.23

Log V

Log2 (max volume)

Loudness function

5.23

0000 0000

0.0

H(Z)

Loudness biquad

Controls shape of

5.23

0x95

b0 = 0000 D513

b0 = 0.006503

loudness curves

b1 = 0000 0000

b1 = 0

b2 = 0FFF 2AED

b2 = –0.006503

a1 = 00FE 5045

a1 = 1.986825

a2 = 0F81 AA27

a2 = –0.986995

Gain (log space)

Loudness function

5.23

0x91

FFC0 0000

–0.5

Offset (log space)

Loudness function

9.23

0x92

0000 0000

Gain

Switch to enable

5.23

0x93

0000 0000

loudness (ON = 1, OFF = 0)

Offset

Provides offset

9.23

0x94

0000 0000

7.4.15.1 Loudness Example

Problem: Due to the Fletcher-Munson phenomena, compensation for low-frequency attenuation near 60 Hz is

desirable. The TAS5548 provides a loudness transfer function with EQ gain = 6, EQ center frequency = 60 Hz,

and EQ bandwidth = 60 Hz.

Solution: Using Texas Instruments TAS5548 GUI tool (downloadable from ti.com), Matlab™, or other signal-

processing tool, develop a loudness function with the parameters listed in Table 10.

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