6
West Mountain Radio
Operating Manual
the difference between the voice and the noise when both are
at equal level and the noise is constantly varying.
When the signal is CW, its intermittent character is sensed and
the CW is passed through. The noise is attenuated. When
the noise is steady, such as a heterodyne from a 40 meter
broadcast station (carrier whistle), it is attenuated greatly to
over 50 dB or about 0.003 times the original value. If the
noise is a moving heterodyne, it is greatly reduced as well, but
not as much as a fixed heterodyne.
Transient sounds are greatly reduced, especially if they are
repetitious. The net effect of the Digital Signal Processor is to
reduce atmospheric noise, static, hiss, ignition noise, power
line noise, carriers, hum, and heterodynes, while passing
voice and CW signals.
The adaptive nature of the noise reduction is apparent by
observing its convergent time. A single audible tone will
vanish in about 1 second. White noise diminishes in 1 to 2
seconds. Typical car noise and emergency alarms take about
2 seconds to reduce.
ClearSpeech Adaptive Speech Filter
The ClearSpeech Adaptive Speech Filter is an algorithm
designed to filter noise from audio signals containing both
speech and noise. It is implemented in a circuit board
containing DSP circuitry and a small audio power amplifier.
Immunity from RF Interference
CLRstereo contains circuitry to reduce interference
from the transmitted radio signal. There are filters on
all input wires and decoupling capacitors at key points
throughout the electronics. There is a ferrite inductor in
series with the positive power lead. Audio level inputs
are via a coupling transformer. This helps reduce any
ground loops.
