Datasheet

B0017-01
Loudness
Biquad
H(z)
Audio OutAudio In
V
VLoudness Function = f(V)
TAS5548
SLES270 –NOVEMBER 2012 www.ti.com
Figure 3-13. Loudness Compensation Functional Block Diagram
Loudness function = f(V) = G × [2
(Log V) × LG + LO
] + O or alternatively,
Loudness function = f(V) = G × [V
LG
× 2
LO
] + 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 3-3. Default Loudness Compensation Parameters
LOUDNESS DESCRIPTION USAGE DATA I
2
C DEFAULT
TERM FORMAT SUB-
HEX FLOAT
ADDRESS
V Max volume Gains audio 5.23 NA NA NA
Log V Log
2
(max volume) Loudness function 5.23 NA 0000 0000 0.0
H(Z) Loudness biquad Controls shape of 5.23 0x95 b
0
= 0000 D513 b
0
= 0.006503
loudness curves b
1
= 0000 0000 b
1
= 0
b
2
= 0FFF 2AED b
2
= –0.006503
a
1
= 00FE 5045 a
1
= 1.986825
a
2
= 0F81 AA27 a
2
= –0.986995
LG Gain (log space) Loudness function 5.23 0x91 FFC0 0000 –0.5
LO Offset (log space) Loudness function 9.23 0x92 0000 0000 0
G Gain Switch to enable 5.23 0x93 0000 0000 0
loudness (ON = 1, OFF = 0)
O Offset Provides offset 9.23 0x94 0000 0000 0
3.7.1 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 3-4.
24 TAS5548 DAP Architecture Copyright © 2012, Texas Instruments Incorporated
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