QS7785 NPC [Nippon Precision Circuits Inc], QS7785 Datasheet - Page 11

• Manufacturer Part Number: QS7785
• Description: 3D 2/4-Channel Stereo Surround Synthesizer
• Manufacturer: NPC [Nippon Precision Circuits Inc]

Center Control
The center signal output on COUT is enabled when
AC is HIGH.
This section describes the output function whereby
fixed frequency sound sources, such as vocal and
speech signals, can be output on the center signal. As
mentioned for “Type C” and “Type D” speaker
arrangements, the center signal can be output by
direct connection to a speaker or by adding the signal
to the front-channel output using a resistor connec-
tion between CIN and COUT.
Using a center speaker
When using a speaker, a capacitor Ca can be con-
nected between LPC and COUT, forming a lowpass
filter. The −3dB cutoff frequency of the filter is given
by the following equation.
Frequencies higher than voice tones are cut from the
signal sent to the center speaker for clear reproduc-
tion of voice-band signals.
Note: Internal resistance value, R1 and R2, may vary ± 15%.
f
=
-------------------------- -
2πCa R1
1
×
Close when AC=H
Open when AC=L
R1:20k
−6dB
LPC
COUT
20
22
G
C
Gain
3dB
Ca
f
L
Center output frequency response
Ra:10k
V(COUT)/V(RIN)@V(LIN)=0
Center output connection
CIN
21
f
H
R2:10k
QS7785PF/CF
Close when MUTE=H
Open when MUTE=L
3dB
R3:10k
or V(FLOUT)
V(FROUT)
Freq.
Adding to the front-channel output
With this connection, the bass frequency components
can be removed from a signal. Capacitors Ca and Cb
and resistor Ra can be connected between CIN and
COUT to form a highpass filter. The −3dB cutoff fre-
quency of the filter is given by the following equa-
tion.
The input signal on CIN is added equally to both
front-channel outputs FLOUT and FROUT. Frequen-
cies lower than voice tones are cut from the signal
added to the front-channel outputs for clear repro-
duction of voice-band signals.
f
f
G
L
=
C
=
10k
10k
=20 log
2πCb(Ra+R2)
--------------------------------------- -
2πCb Ra
1
(
Ra+R2
(
R3
1
V
10k
10k
f
H
REFOUT
=
+
)
2πCaR1
−6dB
R2
1
NIPPON PRECISION CIRCUITS—11
FROUT
FLOUT
26
25
)
Front Right
Speaker
Cnter
Speaker
Front Left
Speaker