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252
Rev. 0.8
The audio deviation should be set as high as possible, with the constraint that the sum of the audio, pilot and
RDS deviation must be 75 kHz or less. Typical settings are 66.25 kHz audio deviation, 6.75 kHz pilot deviation
and 2 kHz RDS deviation.
Example 1:
An application providing a 150 mV
PK
input to the device on RIN/LIN would set Line Attenuation = 00, resulting
in a maximum permissible input level of 190 mV
PK
on LIN/RIN and an input resistance of 396 k
. With 50 µS
pre-emphasis and the limiter disabled, the Line Level would be set to 150 mV
PK
and the source level would be
adjusted down by 13.5 dB to 30 mV
PK
to compensate for pre-emphasis. With the limiter enabled, the input
source can be maintained at 150 mV
PK
, but the line level should be set at 188 mV
PK
to give 2 dB headroom.
Example 2:
An application providing a 1 V
PK
input to the device on RIN/LIN would set Line Attenuation = 11, resulting in a
maximum permissible input level of 636 mV
PK
on LIN/RIN and an input resistance of 60 k
. An external series
resistor on LIN and RIN inputs of 58 k
would create a resistive voltage divider that would keep the maximum
line level on RIN/LIN below 509 mV
PK
to give a 2 dB headroom. With input signal at 509 mV
PK
, 75 µs pre-
emphasis and the limiter enabled, the Line Level can be set to 636 mV
PK
.
2.
Enable the audio dynamic range control
In general the greater the sum of threshold and gain, the greater the perceived audio volume. The following
examples demonstrate minimal and aggressive compression schemes. When using the audio dynamic range
control, care must be taken to configure the device such that the sum of the threshold and gain is zero, or less,
as not to distort or overmodulate. In practice, the sum of the threshold and gain will be less than zero to
minimize the possibility for distortion.
Example 1 (minimal compression):
SETPROPERTY: TX_ACOMP_THRESHOLD = –40 dBFS
SETPROPERTY: TX_ACOMP_ATTACK_TIME = 5 ms
SETPROPERTY: TX_ACOMP_RELEASE_TIME = 100 ms
SETPROPERTY: TX_ACOMP_GAIN = 15 dB
Example 2 (aggressive compression):
SETPROPERTY: TX_ACOMP_THRESHOLD = –15 dBFS
SETPROPERTY: TX_ACOMP_ATTACK_TIME = 0.5 ms
SETPROPERTY: TX_ACOMP_RELEASE_TIME = 1000 ms
SETPROPERTY: TX_ACOMP_GAIN = 5 dB
