Preliminary
HT9015
Compander
In the HT9015, the compressor will take a sig-
nal with a 75dB dynamic range (-5dB to
-80dB), and reduce it to a 37.5dB dynamic
range (-7.5dB to -45dB) by attenuating strong
signals,while amplifying low level signals. The
expander does the opposite in that the 37.5dB
signal range is increased to a dynamic range of
75dB by amplifying strong signals and attenu-
ating low level signals. The 0dB level is inter-
nally set at 316.227mVrms - that is the signal
level which is neither amplified nor attenuated.
See Figure 9 below. Through the action of the
compander, the noise of the transmission me-
dium is constant under -80dBV.
The compander (compressor and expander) is
composed of two variable gain circuits which
provide compression and expansion of the sig-
nal dynamic range. In consideration of the wide
band noise and maximum dynamic range
which exist in the transmission medium, the
general signal handling technique lowers the
general communication quality by reducing the
S/N ratio and generating a clipping phenome-
non. However the compander improves the
communication quality by automatically con-
trolling the gain based on the input signal level
to increase the valid dynamic range and to im-
prove the S/N ratio.
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Figure 9 Illustration of compressed and extended signal
18
April 10, 2000
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
