TAS5508 datasheet(32/105 Pages) TI

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B0017-01

Loudness

Biquad

H(z)

Audio Out

Audio In

Loudness Function = f(V)

2.9.1

Loudness Example

TAS5508

8-Channel Digital Audio PWM Processor

SLES091D – FEBRUARY 2004 – REVISED JULY 2009

www.ti.com

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

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

near 60 Hz. The TAS5508 provides a loudness transfer function with EQ gain = 6, EQ center frequency =

60 Hz, and EQ bandwidth = 60 Hz.

Solution: Using Texas Instruments ALE TAS5508 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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