TAS5508B Datasheet, PDF (34/106 Pages) Texas Instruments – 8-Channel Digital Audio PWM Processor

TAS5508B
8-Channel Digital Audio PWM Processor
SLES162B – DECEMBER 2005 – REVISED APRIL 2006
www.ti.com
2.9 Loudness Compensation
The loudness compensation function compensates for the Fletcher-Munson loudness curves. The
TAS5508B loudness implementation tracks the volume control setting to provide spectral compensation
for weak low- or high-frequency response at low volume levels. For the volume tracking function, both
linear and logarithmic control laws can be implemented. Any biquad filter response can be used to provide
the desired loudness curve. The control parameters for the loudness control are programmable via the I²C
interface.
The TAS5508B 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.
V
Audio In
Audio Out
Loudness
Biquad
H(z)
Loudness Function = f(V)
V
Figure 2-14. Loudness Compensation Functional Block Diagram
B0017-01
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
TERM
DESCRIPTION
V
Log V
H(Z)
Max volume
Log₂ (max volume)
Loudness biquad
LG
Gain (log space)
LO
Offset (log space)
G
Gain
O
Offset
USAGE
Gains audio
Loudness function
Controls shape of
loudness curves
Loudness function
Loudness function
Switch to enable
loudness (ON = 1, OFF = 0)
Provides offset
DATA
FORMAT
5.23
5.23
5.23
I²C
SUB-
ADDRESS
NA
NA
0x95
5.23
25.23
5.23
25.23
0x91
0x92
0x93
0x94
DEFAULT
HEX
FLOAT
NA
0000 0000
b₀ = 0000 D513
b₁ = 0000 0000
b₂ = 0FFF 2AED
a₁ = 00FE 5045
a₂ = 0F81 AA27
FFC0 0000
0000 0000
0000 0000
NA
0.0
b₀ = 0.006503
b₁ = 0
b₂ = –0.006503
a₁ = 1.986825
a₂ = –0.986995
–0.5
0
0
0000 0000
0
34
Description