Datasheet

B0017-01
Loudness
Biquad
H(z)
Audio OutAudio In
V
VLoudness Function = f(V)
TAS5508C
SLES257–SEPTEMBER 2010 www.ti.com
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 × [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 2-6. 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 25.23 0x92 0000 0000 0
G Gain Switch to enable 5.23 0x93 0000 0000 0
loudness (ON = 1, OFF = 0)
O Offset Provides offset 25.23 0x94 0000 0000 0
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.
32 Description Copyright © 2010, Texas Instruments Incorporated
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