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4. MUSIC REPEAT Operation
When the MUSIC REPEAT key is placed ON
while the unit is presently in the PLAY status,
the present music selection (or the next if un-
recorded tape selections) continues to completion,
then the output from pin 13 of PA3010 goes from
Iow to high. After the output of pin 13 has been
held high f.ot 2.5 seconds, the unit returns to the
beginning of that selection and repeats playback.
This operation may be repeated for the same
selection for up to 8 times, after which MUSIC
REPEAT is cleared and a STOP status entered.
out put
The STOP status will also be entered in case the
t
end sensor is activated.
F i g . 1 - 2 3 M U S I C R E P E A T o p e r a t i o n
1.8 DOLBY NR PROCESSOR
The CT-9R and CT-8R both feature type B and
type C Dolby NR processors.
The type C Dolby NR system enables noise to
be reduced by up to 20dB at frequencies above
7l<Ilz. The basic operating principles are the same
as for the type B Dolby NR system, the major
difference lying in the use of two separate pro-
cessor stages (a high level stage and a low level
stage connected in series). Switching to a type
B Dolby NR processor also enables Wpe B encoded
tapes to be played. Block diagxams for encoding
and decoding operations are outlined
in Ftgs.
L-25 and L-26 respectively. The corresponding
input/output
frequency response curves are shown
in Fig. 1-24.
The REC srgnal is passed through a spectral
skewing circuit (see Fig. 1-25) which is an LC
resonator with an for at 2OWlz, and designed to
prevent low to mid-range decoding error (high
level leakage) due to high level signals.
The REC signal is then applied to the lst
processor stage (high level stage) where it is divided
rnto 2 signals, the main signal being passed directly
to adder A, while the main signal is passed via
SCF-1 (side chain filter), arnplifier B and over-
shoot suppressor C before being applied to adder
A where the main and sub signals are recombined.
1 5
......*
Input
Fig. 1-24 InpuVOutputcharacteristic
In addition, the amplifier B output is applied to
rectifier E (non-linear integrating type) via ampli
fier D, the rectified output being applied to VCR-1
(voltage control resistor) of SCF-1. This SCF is a
variable high-pass filter
where the frequency
response is varied according to the VCR value.
The VCR value is increased under low level con-
ditions, and the SCF-1 tumover frequency is
determined by CURI.
The level of the adder A
output will thus be 10dB higher than the main
signal level (around 1.5kHz), and the dynamic
range will be contracted. The VCR value will drop
when the
VCR
control
voltage exceeds the
threshold value, and the SCF-1 turnover frequency
will be increased by C2lC!lR2lVCR-1,
thereby
attenuating low to mid-range signals in the sub-
signal. And since the sub to main signal ratio is
lower at higher input
signal frequencies, the
degree of dynamic range conhaction is smaller.
The adder A output
is applied to the 2nd
processor stage (low level stage) where the signal
whose dynamic range was compressed in the lst
compressor stage is added. In order to further
compress the dynamic range in this 2nd processor
stage, the threshold level of the 2nd processor
VCR-2 control voltage is set below the corespond-
ing level of the 1st processor stage. The 2nd
processor stage also includes an anti-saturation
circuit R. The purlpose of this circuit is to effect
the same improvements as the spectral skewing
circuit.
During playback (se Fig. t-26), the same basic
circuitry is used as in recording mode, but with the
1st and 2nd processor stages in the reverse order.
Since the circuit starts from the output of the
inverter (sub-signal output), a negative feedback
loop is formed with the sub-signal being subtracted
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