Datasheet

f − Frequency − Hz
Gain − dB
10 20k100 1k
G001
20
0
−10
−20
−40
10
−30
10k
TAS5508C
www.ti.com SLES257–SEPTEMBER 2010
Table 2-7. Loudness Function Parameters
LOUDNESS DESCRIPTION USAGE DATA I
2
C DEFAULT
TERM FORMAT SUB-
HEX FLOAT
ADDRESS
H(Z) Loudness biquad Controls shape of 5.23 0x95 b
0
= 0000 8ACE b
0
= 0.004236
Loudness curves b
1
= 0000 0000 b
1
= 0
b
2
= FFFF 7532 b
2
= –0.004236
a
1
= FF01 1951 a
1
= –1.991415
a
2
= 007E E914 a
2
= 0.991488
LG Loudness gain Loudness function 5.23 0x91 FFC0 0000 –0.5
LO Loudness offset Loudness function 25.23 0x92 0000 0000 0
G Gain Switch to enable 5.23 0x93 0080 0000 1
loudness (ON = 1, OFF = 0)
O Offset Offset 25.23 0x94 0000 0000 0
See Figure 2-15 for the resulting loudness function at different gains.
Figure 2-15. Loudness Example Plots
2.10 Dynamic Range Control (DRC)
DRC provides both compression and expansion capabilities over three separate and definable regions of
audio signal levels. Programmable threshold levels set the boundaries of the three regions. Within each of
the three regions, a distinct compression or expansion transfer function can be established and the slope
of each transfer function is determined by programmable parameters. The offset (boost or cut) at the two
boundaries defining the three regions can also be set by programmable offset coefficients. The DRC
implements the composite transfer function by computing a 5.23-format gain coefficient from each sample
output from the rms estimator. This gain coefficient is then applied to a mixer element, whose other input
is the audio data stream. The mixer output is the DRC-adjusted audio data.
There are two distinct DRC blocks in the TAS5508C. DRC1 services channels 1–7 in the 8-channel mode
and channels 1–4 and 7 in the 6-channel mode. This DRC computes rms estimates of the audio data
streams on all channels that it controls. The estimates are then compared on a sample-by-sample basis
and the larger of the estimates is used to compute the compression/expansion gain coefficient. The gain
coefficient is then applied to the appropriate channel audio streams. DRC2 services only channel 8. This
DRC also computes an rms estimate of the signal level on channel 8 and this estimate is used to compute
the compression/expansion gain coefficient applied to the channel-8 audio stream.
Copyright © 2010, Texas Instruments Incorporated Description 33
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