Harman Kardon CD491 - Dolby NR and HX-PRO System Details; Dolby B and C Noise Reduction (NR) Systems; The operating principle of Dolby noise reduction; Dolby HX-Professional Headroom Extension (HX-PRO) System

Bias Fine Trim Feature
The optimal amount of recording bias varies from tape
to tape. The bias fine trim feature is provided to enable
precise adjustment for such variations.
‘The high frequency range tends to be attenuated if the
bias current is higher than the optimum value while it
tends to be boosted if the bias current is less than the
optimum value. Less than optimum bias also increases
the amount of distortion in a recording.
This unit assists the user in determining the precise
amount of bias, and therefore in obtaining the widest
and flattest frequency response.
Operate as follows:
1. Insert a cassette tape in the CASSETTE COMPART-
MENT and press the TAPE SELECTOR button corre-
sponding to the type of tape being used.
2. Depress the TAPE MONITOR switch and make
certain that the TAPE MONITOR indicator illumi-
nates.
3. Press the RECORD and PLAY buttons together to
start recording.
4. Hold the BIAS TONE button in. A 400Hz signal and
a 12.5kHz signal are recorded in the left and right
channels, respectively.
. Compare the left and right channel PEAK LEVEL
METER readings. If the amount of bias is optimum,
the left and right channels will have the same reading.
Turn the BIAS FINE TRIM knob counterclockwise
(toward the direction marked as HI CUT) if the right
channel reading exceeds the left channel reading or
clockwise (toward the direction marked as Hi
BOOST) if the left channel reading exceeds the right
channel reading.
a
If the right channel reading exceeds the left channel
reading:
BIAS FINE TRIM
Turn the knob counterclockwise.
|f the left channel reading exceeds the right channel
reading:
BIAS FINE TRIM
MOT peut 4ni boost
Turn the knob clockwise.
Record Calibration Feature
Each tape has different sensitivity. As a result, a tape
that is recorded at a OdB level may have a playback level
that is either higher or lower than OdB. The record
calibration feature enables the user to precisely adjust
the record/playback level so that both modes correlate,
This is especially important when making Dolby NR
encoded recordings.
Operate as follows:
1, Insert the. cassette tape to be recorded into the CAS-
SETTE COMPARTMENT. Press the TAPE
SELECTOR button according to the tape type.
2. Press the TAPE MONITOR switch and make certain
that the TAPE MONITOR indicator illuminates,
3. Press the RECORD and PLAY button together to
start recording.
4. Hold in the RECORD CALIBRATION button. A
400Hz signal is recorded on each channel.
. If the PEAK LEVEL METERS show OaB, no adjust-
ment is required. If the indicated level is above or
below OdB, adjust the RECORD CALIBRATION
control{s) of the left and right channels using a the
screwdriver provided with your unit. If the indication
of the PEAK LEVEL METER is below OdB, turn the
RECORD CALIBRATION control clockwise to
adjust
to
OdB.
If
the
PEAK
LEVEL
METER
reads
above OdB, turn the RECORD CALIBRATION
control counterclockwise.
a
If the indication is below OdB.
ene (even METER cee cal left right
SSCS) ur ae
i oo i
mat
Turn the controls clockwise,
\f the indication is above OdB.
Peak LeveL METER 06 cal left right
©
‘Turn the controls counterclockwise.
NOTE: Adjustment to OdB may be impossible if the
tape used is old or of poor quality.