TAS5508C datasheet(32/107 Pages) TI

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B0017-01

Loudness

Biquad

H(z)

Audio Out

Audio In

Loudness Function = f(V)

TAS5508C

SLES257 – SEPTEMBER 2010

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The TAS5508C has a single set of loudness controls for the eight channels. In 6-channel mode, loudness

is available to the six speaker outputs and also to the line outputs. The loudness control input uses the

maximum individual master volume (V) to control the loudness that is applied to all channels. In the

192-kHz and 176.4-kHz modes, the loudness function is active only for channels 1, 2, and 8.

Figure 2-14. 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 2-6. Default Loudness Compensation Parameters

LOUDNESS

DESCRIPTION

USAGE

DATA

I2C

DEFAULT

TERM

FORMAT

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

25.23

0x92

0000 0000

Gain

Switch to enable

5.23

0x93

0000 0000

loudness (ON = 1, OFF = 0)

Offset

Provides offset

25.23

0x94

0000 0000

2.9.1

Loudness Example

Problem: Due to the Fletcher-Munson phenomena, we want to compensate for low-frequency attenuation

near 60 Hz. The TAS5508C provides a loudness transfer function with EQ gain = 6, EQ center frequency

= 60 Hz, and EQ bandwidth = 60 Hz.

Solution: Using Texas Instruments ALE TAS5508C DSP tool, Matlab™, or other signal-processing tool,

develop a loudness function with the parameters listed in Table 2-7.

Description

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