Kenwood TS-990S In-Depth Manual page 48

06 DSP
● Line Enhancer Method: NR1
The line enhancer method, which employs a DSP, is widely used for general noise reduction.
The line enhancer method automatically changes the FIR filter characteristics to the frequency components of received
signals. It especially provides high filtering effects on periodic signals such as CW signals and improvement of the S/N
ratio. Because the process automatically passes and emphasizes periodic signals, it is called a line enhancer (line
spectrum enhancer). The line enhancer employs relatively simple signal processing for effect of S/N ratio improvement;
however, it has weak points such as a blurring of sound in weak signal processing in SSB mode. It is positioned in the
TS‑990S as noise reduction to non‑audio‑intended signals.
The graphs below show how the NR1 improves the S/N ratio of a tone signal with the line enhancer method.
● SPAC Method: NR 2
The NR2 is for noise reduction with a speech processing system by using the Autocorrelation function, which is called
SPAC (Speech Processing system by use of the Auto Correlation function).
This system enables to detect periodic signals contained in the received signal and to piece together the periodic
signals detected as the received signal to be reproduced. Consequently, only the periodic signals in the received audio
are highlighted clearly.
The substance of the line enhancer method of NR1 is a filter; however, the approach of NR2 to signal processing is
different from that of the line enhancer method. Therefore, NR2 is effective to signals with a single frequency such as
CW signals. Also, the SPAC method characteristically detects the rising of a signal quickly, so it also delivers an effect to
make attack parts of a CW signal more distinguishable. With these features, the NR2 is a very beneficial function in CW
mode. However, due to its operating principle, for less periodic audio signals, it may generate some noise where periodic
signals join, and the noise may make the audio less clear. In practical operation, we recommend you use the NR1 in
SSB mode and choose the NR1 or the NR2 depending on the circumstances in CW mode.
The NR2 allows the autocorrelation time, which is important for periodic signal demodulation, to be specified in
the range of 2 to 20 ms. The optimum autocorrelation time differs depending on the receive conditions such as the
frequency of the target signal and the noise contained in the received signal. Configure the best autocorrelation time to
receive a signal by receiving the actual signal.
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Fig. 71 Effect of the NR1 with the Line Enhancer Method