TAS5558_15 Datasheet, PDF (44/121 Pages) Texas Instruments – TAS5558 8-Channel HD Compatible Audio Processor with ASRC and PWM Output

TAS5558
SLES273B – APRIL 2013 – REVISED APRIL 2015
7.4.18 Downmix Algorithm and I2S Out
SDIN1
LEFT
CH
RIGHT
CH
COEF
0XE3
COEF
0XE7
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RIGHT
OUT
SDIN4
CENTER
CH
COEF
0XE5
LS
CH
SDIN2
RS
CH
COEF
0XE4
COEF
0XE6
DOLBY
DOWN
MIX
COEF
0XE8
LEFT
OUT
Figure 38. Dolby Downmix
The TAS5558 has an excellent feature that can mix the input signals to create a downmix to make the I2S serial
output which has an SRC that keeps output sample rate at 48KHz irrespective of input sample rate.
Downmix registers are defined as follows:
0xE3 == Coefficient for L and R channels
0xE4 == Coefficient for Center channel
0xE5 == Coefficient for LS for R_out
0xE6 == Coefficient for Rs for R_out
0xE7 == Coefficient for Ls for L_out
0xE8 == Coefficient for Rs for L_out
L _ out = E3 ´ L + E4 ´ C + E7 ´ Ls + E8 ´ Rs
R _ out = E3 ´ R + E4 ´ C + E5 ´ Ls + E6 ´ Rs
L, R, C, Ls, Rs are input cross bar mixer outputs. L, R, C, Ls, Rs are defined as the output of input mixers. L =
Ch1, R = Ch2, C = Ch8, Ls = Ch3, Rs = Ch4, use input mixer to mix any other channels to I2S Out.
(4)
Input Mixers also can be used as other mixers to mix subwoofer channels to I²S out.
By default I²S out has the following values:
L _ out = ^{(L + 0.707 ´ C - 0.707 ´ Ls - 0.707 ´ Rs)}
3.121
(R + 0.707 ´ C - 0.707 ´ Ls - 0.707 ´ Rs)
R _ out =
3.121
test
(5)
7.4.19 Stereo Downmixes/(or Fold-Downs)
7.4.19.1 Left Total/Right Total (Lt/Rt)
Lt/Rt is a downmix suitable for decoding with a Dolby Pro Logic upmixer to obtain 5.1 channels again. Lt/Rt is
also suitable for stereophonic sound playback on a hi-fi or on headphones.
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